1648 


FS  ON  THE  TEACHING 

OF 


ELEMENTARY   CHEMISTRY 


UC-NRLF 


TILDEN 


HINTS 

ON 

THE    TEACHING 

OF 

ELEMENTARY    CHEMISTRY 

IN 

SCHOOLS    AND    SCIENCE    CLASSES     ... 


BY 

WILLIAM  A  TILDEN,  D.Sc.,  F.R.S. 

PROFESSOR  OF  CHEMISTRY  IN  THE  ROYAL  COLLEGE  OF  SCIENCE,    LONDON 
EXAMINER     IN     CHEMISTAY     TO     THE     DEPARTMENT     OF     SCIENCE     AND     ART 


SECOND    EDITION 


LONGMANS,     GREEN,     AND     CO. 

LONDON,  NEW  YORK,  AND  BOMBAY 
1896 

All    rights    reserved 


•L  ft 


BY    THE    SAME    AUTHOR. 


INTRODUCTION  TO  THE  STUDY  OF 
CHEMICAL  PHILOSOPHY.  The  Princi- 
ples of  Theoretical  and  Systematic  Chemistry. 
With  5  Woodcuts.  With  or  without  the 
ANSWERS  of  Problems.  Fcp.  8vo.  4.$-.  6d. 

PRACTICAL  CHEMISTRY.  The  Principles 
of  Qualitative  Analysis.  Fcp.  8vo.  is.  6d, 


LONGMANS,    GREEN,    &    CO. 

LONDON,  NEW  YORK,  AND  BOMBAY. 


PREFACE 


THE  issue  of  the  new  Syllabus  of  Inorganic  and 
Organic  Chemistry  by  the  Department  of  Science 
and  Art  marks  a  very  important  advance  in 
the  history  of  the  teaching  of  these  subjects  in 
this  country.  In  this  Syllabus  the  treatment 
of  Chemistry  from  the  theoretical  side  remains 
necessarily  at  the  discretion  of  the  teacher,  though 
from  the  order  in  which  the  subdivisions  of  the 
matter  for  treatment  are  placed,  it  is  obvious  that, 
in  the  early  stages  especially,  it  is  considered  desir- 
able to  keep  theory  in  a  subordinate  position,  and  to 
make  use  of  it  only  when  a  sufficient  foundation 
of  fact  has  been  duly  acquired  by  the  pupil. 
According  to  the  experience  of  the  Author,  it  is 
scarcely  possible  to  use  a  purely  inductive  method 
in  dealing  with  young  students ;  but,  though  this 
may  be  admitted,  the  necessity  of  clearly  distin- 
guishing fact  from  hypothesis  requires  to  be 
established  far  more  definitely  than  at  present  in 
the  minds  of  a  large  proportion  of  the  teachers 


iv     Teaching  of  Elementary  Chemistry 

whose  pupils  present  themselves  for  the  examina- 
tions of  the  Department 

In  the  earliest  stages,  the  learner's  attention 
and  energy  are  usually  wholly  used  up  in  the 
process  of  exact  observation.  To  see  and  accu- 
rately record  the  whole  of  a  given  phenomenon 
is  enough  for  young  boys  and  girls,  and,  until 
sufficient  practice  and  experience  in  this  direction 
have  been  gained,  it  is  a  better  educational  exercise 
than  the  attempt  to  solve  problems  which,  to 
render  them  simple  enough,  require  the  neglect  of 
part  of  the  phenomena.  For  example,  the  investi- 
gations of  the  changes  which  occur  when  a  piece 
of  sheet  copper  is  heated  in  the  air  requires  for  a 
complete  answer  observations  (a)  on  the  iridescent 
colours  first  visible,  (b)  the  black  coating  which 
succeeds,  (c}  the  red  lining  to  the  scales  which  may 
be  separated  on  cooling,  (d)  the  temperature  at 
which  these  changes  occur,  *{^)  the  alteration  in 
weight  of  the  mass,  (/)  changes  in  the  surrounding 
air,  &c.  Observation  of  all  these  facts  is  possible 
even  for  the  beginner  ;  but  when  he  is  in  possession 
of  the  whole,  he  would  be  a  wonderful  boy  in- 
deed who  could,  without  assistance,  infer  that  the 
products  contain  oxygen  as  well  as  copper,  and 
that  there  are  two  oxides  of  copper  of  definite 
composition,  to  say  nothing  about  the  colours  of 
thin  films. 

Chemistry  is  a  science  which,    in  its  modern 
form,  has  sprung  up    almost   entirely  within  the 


Preface  v 

memory  of  living  man,  and  its  boundaries,  already 
far  reaching,  are  being  rapidly  extended  year  by 
year,  and  even  month  by  month,  by  the  labours 
of  an  army  of  workers.  This  condition  of  growth 
constitutes  a  feature  of  the  science  which  should 
render  it  as  a  study  attractive  in  no  ordinary  degree  ; 
and  the  teacher  who  desires  to  make  use  of  it  as 
an  effective  educational  agent  must  devote  some 
part  of  his  time  to  extending  and  consolidating 
his  own  knowledge.  Not  that  the  very  latest 
discovery  is  necessarily  more  important  than  many 
of  the  facts  which  have  been  long  familiar,  and 
the  teacher  ought  to  be  careful  to  exercise  due 
disci  etion  in  communicating  to  a  class  of  young 
pupils  the  most  recent  results  of  observation, 
ler>t  their  sense  of  proportion  should  be  unequal 
to  the  strain  of  distinguishing  the  important 
from  the  comparatively  unimportant.  The  dis- 
covery of  argon  in  the  atmosphere  twelve  months 
ago  possesses  the  greatest  interest  for  the  advanced 
student ;  but  oxygen  still  ranks  higher  in  im- 
portance, from  all  practical  as  well  as  theoretical 
points  of  view,  than  the  newly  discovered  gas. 

In  the  new  Syllabus  issued  by  the  Department 
the  most  important  changes  will  be  noticed  in  the 
part  which  relates  to  the  practical  examinations. 
Scientific  chemistry  is  based  almost  wholly  upon 
observation  and  experiment,  and  the  practical  study 
of  this  science  is  one  of  the  most  useful  means  of 
developing  the  faculties  of  observation.  But  even 


vi     Teaching  of  Elementary  Chemistry 

in  the  teaching  of  analytical  chemistry,  which  is 
especially  dependent  upon  the  practice  of  careful 
and  exact  observation,  the  '  crammer '  has  been 
at  work  to  such  an  extent  as  largely  to  destroy 
the  educational  value  of  this  important  and  in- 
teresting subject,  and,  instead  of  being  made  to 
record  accurately  the  results  of  his  own  obser- 
vations, the  pupil  is  too  often  allowed  to  learn  by 
rote  tables  or  schemes  of  analysis,  and  is  led  to 
state,  not  what  he  sees,  but  what  the  book  tells  him 
he  ought  to  see.  A  form  of  examination  question 
used  by  the  Author  which  requires  the  candidate 
to  describe  some  operation  which  he  has  himself 
conducted  has  often  received  answers  so  remarkable 
as  to  show  that  the  faculty  of  observation  is  in 
some  cases  almost  extinguished  by  the  habit  of 
blind  reliance  upon  a  printed  text. 

The  following  chapters  contain  the  substance 
of  a  short  course  of  Lectures  given  in  July  last  to 
the  class  of  Teachers  assembled  for  instruction  at 
the  Royal  College  of  Science  ;  and  in  the  belief  that 
the  hints  contained  in  them  would  be  useful  to 
others  engaged  in  preparing  for  the  May  exami- 
nations, as  well  as  to  Teachers  of  Elementary 
Classes  generally,  they  are  now  offered  in  a  slightly 
amplified  form,  and  with  a  little  more  detail  than 
is  possible  in  presenting  the  same  subjects  in  the 
lecture-room. 

ROYAL  COLLEGE  OF  SCIENCE,  LONDON  : 
'September  1895. 


CONTENTS 


CHAPTER  PAGE 

I.     OBSERVATION— QUALITATIVE         ....        I 
II.      OBSERVATION— QUANTITATIVE          .          .          «     .      12 

III.  OBSERVATION— QUANTITATIVE     .       ..          „          ,      21 

IV.  CHEMICAL       EQUIVALENTS  —  THE       LAW        OF 

VOLUMES  .          .          .          ; '         .          .     .      31 

NOTE  TO  CHAPTER  IV.  .          .        •/;"    ,          .      44 

CHRONOLOGICAL       TABLE,          FOUNDERS         OF 

CHEMISTRY     .  .  .          <          .  .  .42 

V.      MOLECULAR  WEIGHTS  AND   FORMULAE    .  .      .      46 

VI.     ATOMIC  WEIGHTS— CLASSIFICATION      .          .          .55 

APPENDIX  .          .          .          .          .         V        .     .      70 


f  *  OF  THE  >v 

V  »F  J 

^V^CAUFORN^-^^ 


(UNIVERSITY) 


HINTS    ON    THE    TEACHING 

OF 

ELEMENTARY  CHEMISTRY 

CHAPTER    I 

OBSERVATION-QUALITATIVE 

THE  history  of  chemistry  affords  numerous  in- 
stances of  fallacies  originating  as  a  consequence 
of  imperfect  observation.  In  some  cases  such 
fallacies  have  been  received  as  articles  of  belief 
almost  undisputed  for  centuries.  The  doctrine  of 
the  transmutability  of  metals,  and  especially  of  the 
base  metals,  into  silver  and  gold  is  an  example  of 
this  kind.  It  is  a  fact  that  almost  any  sample  of 
lead,  submitted  to  the  process  of  cupellation,  yields 
a  little  bead  of  silver  which  often  contains  gold. 
It  was  not  an  unnatural  hypothesis  that  this  silver 
somehow  originated  in  a  change  brought  about  in 
the  lead  by  the  action  of  heat  ;  and  since  in  different 
operations  the  yield  of  precious  metal  was  known 

B 


2       Teaching  of  Elementary  Chemistry 

to  vary,  it  seemed  likely  that  by  suitably  changing 
the  conditions  complete  transmutation  might  be 
brought  about. 

The  doctrine  of  Phlogiston,  again,  seemed  to 
supply  all  that  was  wanted  to  explain  the  process 
of  combustion  and  to  bring  under  a  common  theory 
the  phenomena  of  burning,  rusting  of  metals, 
decay  of  wood,  and  fermentation  of  saccharine 
fluids.  When  a  piece  of  wood  or  charcoal  k 
burned,  the  theory  taught  that  the  escaping 
phlogiston  was  the  cause  of  the  appearance  of  fire, 
the  calx  remaining  in  the  ashes  upon  the  hearth. 
Metallic  iron  exposed  to  the  air  loses  its  phlogiston, 
and  becomes  transformed  into  a  calx  more  copious 
than  that  of  charcoal.  The  latter,  then,  is  rich  in 
phlogiston,  and  ought  to  be  able  to  impart  some  of 
it  to  the  calx  of  iron,  and  so  restore  it  to  the  metallic 
or  reguline  condition,  and  this  it  does  when  iron 
ore  cr  rust  is  heated  with  charcoal  All  this  is 
true  as  far  as  it  goes,  but  the  defect  in  the  theory 
was  that  it  did  not  take  cognisance  of  the  fact  that 
when  metals  are  calcined  the  resulting  calx  is 
heavier  than  the  metal. 

Another  most  instructive  example  of  bad  ob- 
servation, and  consequent  erroneous  theory,  is 
exhibited  in  the  history  of  the  element  we  now 
call  chlorine.  This  gas  was  discovered  by  Scheele 
in  1774,  and  called  by  him  dephlogisticated  muriatic 
acid.  In  this  he  was  quite  right,  for  such  a  de- 
signation means  that  the  new  gas  consisted  of 


Observation —  Qualitative  3 

muriatic  acid  deprived  of  its  inflammable  principle. 
Berthollet,  however,  concluded  from  his  experi- 
ments that  this  body  was  composed  of  muriatic 
acid  and  oxygen,  and  for  a  long  time  it  was 
thought  that  the  hydrogen,  which  was  undoubtedly 
procurable  from  muriatic  acid  by  the  action  of 
metals  upon  the  gas,  was  due  to  the  accidental 
presence  of  water. 

Sir  Humphry  Davy  established  the  elemental 
character  of  the  substance,  and  gave  it  the  name 
chlorine,  which  refers  solely  to  the  yellowish-green 
colour  of  the  gas,  and  not  to  any  hypothesis  as  to 
its  nature.  But  Davy  succeeded  only  very  gra- 
dually in  getting  rid  of  errors  arising  from  the 
presence  of  moisture  in  the  imperfectly  dried  gas. 
The  principle  adopted  in  his  researches  was  the 
very  simple  one  which  consists  in  attacking  the 
point  in  dispute  directly.  The  question  was 
whether  *  oxymuriatic  acid '  contained  oxygen, 
and  this  he  answered  by  a  series  of  experiments  in 
which  he  proved  that  metals,  charcoal,  phosphorus, 
and  other  bodies  heated  in  the  gas  give  compounds 
recognisable  as  muriates,  but  never  as  oxides  ;  and  he 
pointed  out  that  the  presence  of  oxygen  or  of  hydro- 
gen, or  phlogiston,  '  or  of  other  principles,  should 
not  be  assumed  where  they  cannot  be  detected.' ! 

Among  the  chemists  of  the  past  there  is  none 
whose  writings  are  more  instructive,  or  whose  fame 

1  For  a  complete  account  of  Davy's  work  on  Chlorine,  see 
•Alembic  Club  Reprints,'  No.  9;  W.  F.  Clay,  Edinburgh. 

B  2 


4  •.;   Teaching  of  Elementary  Chemistry 

is  likely  to  be  more  enduring,  than  the  industrious 
Scheele.  And  the  reason  of  this  is  that  his  work 
was  almost  wholly  experimental.  As  he  himself 
says, '  Conjectures  can  determine  nothing  with 
certainty  ;  at  least  they  can  only  bring  small  satis- 
faction to  a  chemical  philosopher  who  must  have 
his  proofs  in  his  hands/  *  Observation  and  experi- 
ment constitute  the  first  and  the  most  important 
business  of  all  students  of  chemistry  ;  but,  that  they 
may  be  fruitful,  observation  and  experiment  alike 
must  be  carried  on  not  listlessly,  carelessly,  with 
'  lack-lustre  eye/  but  with  concentrated  attention 
and  senses  awake  and  active. 

With  all  the  accumulated  experiences  of  the 
past,  the  art  of  observation  is,  however,  still  imper- 
fectly learned,  and  the  chemical  journals  teem  with 
descriptions  of  phenomena  or  of  substances  which 
are  either  incomplete  or  inaccurate,  or  even  wholly 
erroneous.  Writers  of  text-books  are  also  far  from 
blameless  in  this  matter,  and  the  inability  on  the 
part  of  students  to  describe  correctly  even  very 
simple  things  is  often  as  much  due  to  the  per- 
petuation of  false  statements  in  the  books  as  to 
want  of  attention  or  of  skill  on  the  part  of  the 
student.  One  of  the  most  flagrant  cases  is  the 
description  of  the  usual  process  for  the  production 
of  sulphur  dioxide.  A  well-known  text-book 

1  See  Scheele's  *  Chemical  Treatise  on  Air  and  Fire,'  of  which 
the  most  interesting  part,  relating  to  the  discovery  of  oxygen,  is 
translated  into  No.  8  of  the  'Alembic  Club  Reprints,'  already 
referred  to. 


Observation  — Qualitative  5 

contains  the  following  statement :  '  This  gas  is 
prepared  by  the  action  of  hot  concentrated  sul- 
phuric acid  upon  copper  turnings. 

Cu  +  2H2SO4  =  CuSO4  +  2H2O  +  SO2.' 

That  is  the  whole  of  the  explanation  given 
in  this  case.  An  observer  of  the  process,  how- 
ever, cannot  fail  to  see  that,  so  soon  as  the  action 
commences  and  the  gas  begins  to  escape,  the 
copper  becomes  black  ;  but  the  equation  gives  no 
explanation  of  this  fact,  and  students  are  actually 
led  to  believe  that  the  residue  ought  to  be  blue. 
According  to  the  author's  experience,  candidates 
at  examinations  in  which  a  question  occurs  as  to 
the  action  of  sulphuric  acid  upon  copper  do  fre- 
quently make  the  statement  that  the  residue  is 
blue.  Nor  are  students  alone  liable  to  fall  into 
this  error.  A  teacher  once  seriously  proposed  in 
the  author's  presence  to  assist  the  memory  by 
writing  chemical  equations  in  chalks  coloured  so 
as  to  recall  the  appearance  of  the  several  materials 
concerned.  Selecting  the  equation  referred  to  by 
way  of  illustration,  he  wrote  the  Cu  in  red,  the, 
H2SO4  in  white,  and  the  CuSO4  in  blue  chalk, 
ignorant  or  forgetful  of  the  fact  that  CuSO4  is  a 
white  substance. 

The  difficulty  of  making  exact  observations  of 
comparatively  simple  facts  is  daily  illustrated  by 
the  reports  of  the  law  courts,  where  different  wit- 
nesses, actuated,  we  must  believe,  in  many  cases 


6       Teaching  of  Elementary  Chemistry 

by  no  dishonest  motive,  often  give  wholly  contra- 
dictory testimony  as  to  occurrences  of  the  most 
ordinary  kind.  Most  people  are  also  usually  in- 
capable of  discriminating  objects  unless  they  differ 
enormously  in  size  or  colour.  This  is  illustrated 
by  the  common  names  which  have  been  applied 
for  centuries  to  many  familiar  plants.  There  is, 
for  example,  the  greater  celandine  and  the  lesser 
celandine,  which  have  little  resemblance  to  each 
other  beyond  the  colour  of  the  flowers.  The  plants 
called  water-lilies,  again,  have  no  botanical  con- 
nection with  true  lilies,  neither  do  the  flowers 
resemble  those  of  the  lily.  For  a  long  time  there 
was,  and  there  probably  still  exists,  confusion  in 
the  minds  of  the  majority  of  people  as  to  the  two 
forms  of  electric  light  and  the  '  incandescent '  gas- 
burners  now  so  common.  Any  kind  of  bright  light 
seems  to  be  sufficient  to  deceive  the  untrained  eye. 
In  order  to  cultivate  the  powers  of  observa- 
tion, various  branches  of  natural  science  have  been 
brought  into  use  in  schools,  but  none  seem  to 
present  so  many  advantages  as  are  offered  by 
chemistry  when  rightly  taught.  As  a  science 
based  entirely  upon  the  results  of  observation  and 
experiment,  it  is  only  by  making  experiment  a 
principal  feature  of  the  system  of  instruction  that 
these  advantages  can  be  secured.  The  observations 
and  experiments  must  also,  as  far  as  possible,  be 
the  work  of  the  pupil  and  not  of  the  teacher,  and 
therefore  exercises  undertaken  should  be  in  the 


* 


Observation  —  Qualitative 


first  instance  of  the  simplest  possible  character, 
and  graduated  so  as  to  lead  on  to  more  difficult 
operations,  which  should  only  be  undertaken  after 
some  time  and  after  demonstration  by  the  teacher. 
It  is  a  mistake  to  suppose  that  the  great  theories 
of  chemistry  can  be  established  by  experiments 
conducted  wholly  by  beginners,  but  with  due  pre- 
liminary instruction  the  more  advanced  student 
may  get  a  long  way  in  this  direction. 

The  object  of  the  following  series  of  exercises 
is  merely  to  suggest  to  teachers  the  kind  of  practi- 
cal work  which  may  be  advantageously  done  by 
the  pupil,  and  to  show  in  a  general  way  how  he 
may  proceed  from  very  simple  operations  to  work 
of  a  more  complex  character. 

The  earliest  examples  provide  material  for 
observation  without  requiring  more  than  care  and 
attention.  The  teacher  will  have  no  difficulty  in 
devising  an  extended  and  almost  infinite  variety 
of  such  simple  exercises.  It  will  be  necessary  to 
insist  upon  a  written  account  of  each  experiment 
made  by  the  student,  with  a  statement  in  his  own 
words  of  what  he  sees,  without  at  first  requiring  any 
theoretical  explanation  or  discussion.  It  will  often 
be  advantageous  to  supply  materials  with  which 
the  student  is  not  already  familiar.  When  his 
observations  have  been  successfully  recorded,  the 
teacher  may,  if  he  thinks  proper,  tell  him  the 
composition  of  the  substance  and  explain  the  nature 
of  the  changes  which  he  has  noticed, 


8       Teaching  of  Elementary  Chemistry 

EXPERIMENTS  TO  BE  DON£  BY  EACH  PUPIL 

I.  Observation  of  the  action  of  heat  supplied  by 
the  gradual  application  of  a  Bunsen  flame  to  a  dry 
test-tube  containing  a  little  of  the  substance. 

Any  of  the  following  or  other  substances  may 
be  tried  :  Mercuric  oxide,  red  lead,  lead  nitrate, 
potassium  chlorate,  potassium  nitrate,  ammonium 
nitrate,  ammonium  chloride,  mercuric  iodide. 

Gases  evolved  may  be  tested  for  as  follows : 

(1)  Notice  colour,  appearance  of  fumes,  odour. 

(2)  Apply  lighted  wax  taper  first  at  the  mouth 
of  the  tube,  then  pushed  inside. 

(3)  Hold  in   the   gas   strips   of  red   and  blue 
litmus  paper,  moistened  with  water. 

(4)  Hold  within  the  tube  a  drop  of  clear  lime 
water  at  the  end  of  a   narrow   glass   tube,   then 
gently  suck  for  a  moment  at  the  open  end  of  the 
tube  so  as  to  draw  up  the  drop. 

This  series  of  tests  is  not  intended  to  enable 
the  pupil  to  identify  the  gas,  for  that  is  a  matter 
of  comparatively  small  importance  at  this  stage. 
After  observations  have  been  correctly  recorded, 
the  teacher  may  suggest  to  the  pupil  other  experi- 
ments which  appear  to  him  desirable,  such  as  the 
collection  of  the  gas  in  bulk  or  further  examination 
of  the  residue. 

Some  of  the  substances  mentioned  in  the  above 
list  will  afford  opportunities  of  testing  the  genuine- 
ness and  completeness  of  the  student's  work.  For 


Observation — Qualitative  9 

example,  he  may  have  read  or  learned  that  mercuric 
oxide  gives  off  oxygen  and  mercury  when  heated, 
but  unless  he  has  tried  the  experiment  or  seen  it 
tried,  he  could  not  guess  that  the  powder  would 
become  black  while  hot,  and  that  at  a  high  tempe- 
rature it  would  give  a  yellowish-coloured  gas  and 
a  small  yellow  sublimate  upon  the  sides  of  the 
tube,  owing  to  the  trace  of  nitrate  which  the  com- 
mercial red  oxide  invariably  contains. 

II.  Crystallisation    of  salts  from    water,    and 
recognition  of  crystalline  form,  or  at  least  differen- 
tiation of  one  sort  of  crystal  from  another. 

For  example,  make  strong  solutions  of  potas- 
sium nitrate  and  ammonium  chloride  in  hot  water, 
and  pour  into  separate  watch-glasses.  On  cooling 
the  long  prisms  of  the  nitre  are  easily  distinguished 
from  the  fern-leaf  forms  of  the  sal  ammoniac. 
Similarly  alum,  lead  nitrate,  and  barium  nitrate 
will  yield  regular  octahedrons  and  dodecahedrons, 
and  intermediate  forms  distinct  enough  to  be 
readily  visible  and  easily  sketched.  Other  salts 
which  crystallise  from  hot  water  are  potassium 
chlorate,  sodium  nitrate,  magnesium  and  zinc 
sulphates,  copper  sulphate,  chrome  alum,  potas- 
sium dichromate,  &c. 

III.  Precipitates  to  be  distinguished  by  differ- 
ences of  density  or  consistence.    The  following  are 
white  precipitates  differing  in  character:  solution 
of  alum  mixed  with  ammonia  gives  a  gelatinous 
precipitate ;    calcium    chloride  with   carbonate   of 


io     Teaching  of  Elementary  Chemistry 

ammonia  a  flocculent  precipitate  which  becomes 
sandy  on  heating  or  after  standing;  calcium 
chloride  with  dilute  sulphuric  acid  a  mass  of  minute 
crystalline  needles ;  barium  chloride  with  dilute 
sulphuric  acid  a  fine  powder  some  of  which  may 
remain  suspended  a  long  time ;  silver  nitrate  with 
a  chloride  a  white  precipitate  which  curdles  and 
on  exposure  to  daylight  assumes  a  purple  tint,  &c. 

In  like  manner  arsenious  sulphide,  lead  chro- 
mate,  zinc  chromate,  stannic  sulphide,  silver  iodide 
are  examples  of  precipitates  which  have  a  yellow 
colour,  but  differ  in  tint  and  density. 

IV.  The  action  of  strong  sulphuric  acid  upon  sub- 
stances resulting  in  the  evolution  of  gas. 

The  following  examples  will  serve  :  common 
salt,  potassium  nitrate,  red  lead,  potassium  iodide, 
sodium  sulphite,  sodium  formate. 

A  few  grams  of  the  substance  may  be  placed 
in  a  test-tube  and  strong  sulphuric  acid  added  in 
quantity  sufficient  to  make  a  fluid  paste.  If  heat 
is  applied  it  will  be  well  to  caution  young  students 
as  to  the  corrosive  nature  of  the  liquid,  and  direct 
them  to  turn  the  open  mouth  of  the  tube  away 
from  their  own  faces  and  from  the  persons  of  their 
neighbours.  The  evolved  gas  may  be  tested  as 
already  described  under  Section  I. 

In  addition  to  such  exercises  as  the  foregoing, 
specimens  of  well-crystallised  compounds  such  as 
potassium  iodide,  alum,  sugar,  zinc  sulphate,  or  of 
minerals  such  as  galena,  fluorspar,  pyrites,  calcite, 


Observation — Qualitative  1 1 

or  specular  iron  may  be  given  to  be  drawn  and 
described.  And  when  qualitative  analysis  is  begun, 
the  pupil  should  be  taught  in  every  case  to  write 
doivn,  before  applying  tests >  an  account  of  the  appear  - 
ance  and  more  obvious  characters  of  the  substance 
analysed. 


1 2     Teaching  of  Elementary  Chemistry 


CHAPTER   II 

OBSER  VA  T1ON—Q  UANTITA  TIVE 

QUANTITATIVE  experiments  may  be  gravimetric 
or  volumetric  ;  that  is,  they  may  take  the  form  of 
measurements  of  weight  or  of  volume.  Contrary 
to  general  belief,  quantitative  work  may  be  done 
with  very  simple  and  inexpensive  appliances,  and 
in  the  hands  of  even  young  students  results  may  be 
obtained  which  closely  accord  with  theory.  It  is, 
however,  advisable  in  the  first  instance  to  set 
exercises  to  be  done  independently  of  theory  until 
a  series  of  experiments  has  given  concordant 
results,  showing  that  the  pupil  has  acquired  suffi- 
cient skill  to  be  allowed  to  test  for  himself  some 
general  law  which  he  has  already  learnt. 

The  balance  shown  in  the  figure  may  be 
obtained  of  several  instrument  makers  for  about 
2js.  6d.y  and  a  box  of  weights  ranging  from  100 
grams  to  I  milligram  costs  6s. 

The  simplest  quantitative  experiments  are 
those  in  which  a  gain  or  a  loss  of  weight  of  a 
single  object,  such  as  a  crucible,  has  to  be  recorded. 
The  following  are  examples  of  the  kind  of  experi- 


Observation — Quantitative  1 3 

ment  referred  to.  They  can  all  be  done  by 
beginners  with  very  slight  supervision  and  with 
satisfactory  results.  It  is  not  necessary  to  weigh 
to  a  smaller  subdivision  than  'Oi  gram. 

I.  Formation  of  metallic  oxides  and  sulphides. — 
Magnesium  may  easily  be  converted  into  the  oxide 
by  ignition  in  air,  but  to  avoid  loss  it  must  be 
heated  in  a  covered  crucible.  A  clean  '  half-ounce* 


FIG.  i 

covered  porcelain  crucible  should  be  placed  on  the 
left-hand  pan  of  the  balance,  and  counterpoised  by 
putting  small  shot  into  the  lid  of  a  pill-box  placed 
in  the  opposite  pan.  About  15  centimetres  of 
magnesium  ribbon  rubbed  clean  with  sand-paper 
is  then  coiled  up  in  the  crucible,  and  its  weight 
noted.  It  should  weigh  *3  to  '4  gram.  The  cruci- 
ble is  then  placed  on  a  wire  and  tobacco  pipe 


14     Teaching  of  Elementary  Chemistry 

triangle  supported  on  a  tripod  or  retort  stand 
ring  over  a  Bunsen  burner.  The  flame  is  then 
.gradually  applied  till  the  bottom  of  the  crucible 
is  red-hot.  The  lid  may  be  lifted  slightly  from 
time  to  time,  and  in  about  a  quarter  of  an  hour  the 
glowing  of  the  metal  due  to  combustion  will  have 
ceased  and  a  grey  mass  will  remain.  The  lid 
should  then  be  removed  and  a  strong  heat  applied 
a  little  longer  till  the  mass  becomes  white.  I  gram 
of  magnesium  gives  r66  gram  of  the  oxide.  In  a 


FIG.  2 

test  experiment  conducted  as  above,  -39  gram  gave 
•65  gram  of  oxide.  This  is  in  the  proportion  of 
i  to  r66. 

Copper  may  be  readily  converted  into  the  oxide ; 
but  as  a  simple  roasting  process  would  occupy  too 
much  time,  it  is  best  to  convert  the  metal  first  into 
nitrate,  which  is  decomposed  by  subsequent  heating. 
Counterpoise  a  crucible  as  before,  weigh  out  about 
half  a  gram  of  thin  sheet  or  wire,  add  to  it  five 
or  six  drops  of  ordinary  strong  nitric  acid,  cover 


Observation — Quantitative  1 5 

the  crucible  and  set  it  in  a  warm  place  till  a  dry 
green  mass  remains.  Then  heat  over  the  Bunsen 
flame  gradually  to  redness.  The  resulting  oxide 
should  of  course  be  black  and  show  no  signs  of 
unchanged  metal.  Should  any  unchanged  metal 
be  suspected,  a  few  more  drops  of  nitric  acid 
should  be  added  and  the  process  repeated.  Iron 
and  tin  may  be  dealt  with  in  the  same  way. 

i  gram  of  copper  gives  1-25  gram  oxide 
i  gram  of  iron  „     1*43       „ 

I  gram  of  tin  „     1*27       „ 

Copper  may  also  be  converted  into  sulphide, 
by  heating  it  with  sulphur.  A  counterpoised  co- 
vered crucible  containing  about  I  gram  of  flowers 
of  sulphur  is  placed  over  the  Bunsen  flame  and 
heated  strongly  till  the  vapour  of  sulphur  is  seen 
escaping  round  the  lid.  A  weighed  piece  of 
copper  (about  *5  gram)  is  then  dropped  into  the 
crucible,  the  lid  being  lifted  only  slightly  and  im- 
mediately replaced.  The  heating  is  continued  till 
the  excess  of  sulphur  is  completely  volatilised. 
The  crucible  is  then  allowed  to  cool,  and  when  cold 
-is  weighed.  A  small  quantity  of  sulphur  should 
be  added  to  the  contents  of  the  crucible,  which 
should  be  rapidly  heated  again  to  redness,  cooled 
and  reweighed.  The  second  weight  should  be  the 
same  as  the  first. 

For  the  success  of  this  experiment  the  air  must 
be  excluded  as  much  as  possible  from  the  crucible. 


1 6     Teaching  of  Elementary  Chemistry 

The  lid  must  therefore  not  be  removed  while  the 
sulphide  contained  in  the  crucible  is  still  hot.  A 
good  way  of  preventing  access  of  air  is  to  finish 
the  heating  in  an  atmosphere  of  coal  gas  supplied 
through  a  tobacco  pipe,  attached  to  a  rubber  tube, 
and  having  the  bowl  inverted  over  the  crucible. 
The  escaping  gas  burns  with  a  luminous  flame 
round  the  top  of  the  crucible.  I  gram  of  copper 
should  theoretically  give  1*25  gram  of  sulphide. 


FIG.  3 

An  experiment  conducted  as  described  gave  1*26 
gram. 

II.  Decomposition  of  compounds  by  heat. — Pro- 
ceeding in  a  similar  manner,  quantitative  estima- 
tions may  be  made  of  the  products  of  various 
chemical  decompositions  produced  by  heat  in  which 
a  fixed  residue  remains.  For  example,  potassium 
chlorate,  heated,  leaves  potassium  chloride  ;  magne- 
sium carbonate  and  zinc  carbonate  leave  a  residue 


Observation  —  Quantitative  1  7 

of  oxide  ;  crystallised  sulphates  of  copper  and 
other  metals  lose  their  water  and  leave  anhydrous 
sulphates.  Few  remarks  are  necessary  in  con- 
nection with  such  experiments  as  these.  Salts 
which  are  liable  to  crackle  or  decrepitate  must 
of  course  be  heated  in  a  closely  covered  crucible. 
Copper  sulphate,  magnesium  sulphate,  zinc  sul- 
phate, and  gypsum  require  to  be  heated  only  very 
gently  by  means  of  a  rose  burner  placed  some 
three  inches  below  the  bottom  of  the  crucible. 
Commercial  carbonates  of  zinc  and  magnesium 
have  a  nearly  constant  composition  corresponding 
respectively  to  the  formulae  ZnCO3.  Zn  (HO)2.  H2O 
and  3MgCO3.  Mg(HO)2.  4H2O. 

One  gram  of  crystallised  copper  sulphate  should 
yield  '64  gram  of  anhydrous  sulphate.  An  expe- 
riment gave  i  '39  gram,  from  2*16  grams,  which 
corresponds  with  theory.  The  residue  was  slightly 
grey. 

By  such  exercises  as  the  foregoing,  varied  and 
repeated  according  to  the  discretion  of  the  teacher, 
the  student  may  be  shown  that  he  can  for  himself 
verify  the  fundamental  law  of  chemistry  —  namely, 
the  Law  of  Definite  Proportions,  wrhich  asserts  that 
every  chemical  compound  has  a  fixed  and  definite 
composition.  The  experimental  method  may  after 
these  exercises  be  modified  so  as  to  show  that  the 
same  results  may  be  obtained  though  the  materials 
pass  through  a  different  series  of  processes. 

III.  Treatment  of  precipitates.  —  As  an  example 


(  UNIVERSITY) 
V  fi^.s^.       y 


1 8     Teaching  of  Elementary  Chemistry 

a  piece  of  clean  iron  wire  not  more  than  *5  gram 
in  weight  may  be  dissolved  in  a  half-pint  beaker 
by  a  few  cubic  centimetres  of  a  mixture  of  hydro- 
chloric with  a  little  nitric  acid.  The  solution 
is  then  diluted  with  water  and  excess  of  solu- 
tion of  ammonia  added,  the  precipitate  filtered  off, 
the  filter  drained,  dried,  and  burnt  to  ashes  in 
a  counterpoised  crucible.  The  filter  ash  may  be 
neglected.  By  this  process  also  it  may  be  shown 
that  I  gram  of  iron  gives  1-43  gram  of  the  red  oxide. 

In  order  to  prove  to  the  pupil  that  it  is  usually 
necessary  to  wash  precipitates,  the  same  experiment 
may  be  performed  with  the  substitution  of  caustic 
soda  for  ammonia.  After  weighing  the  oxide  of 
iron,  add  some  boiling  water  to  the  contents  of  the 
crucible,  let  the  oxide  settle,  and  pour  off  the  water. 
After  repeating  this  once  or  twice,  dry  the  whole 
and  weigh  again.  The  weight  will  be  slightly 
reduced,  and  nearer  to  the  theoretical  amount. 
The  washings  will  turn  red  litmus  paper  blue. 

IV.  Replacement  of  metals  by  one  another. — A 
clean  piece  of  zinc  foil  immersed  in  a  somewhat 
dilute  (2  to  5  per  cent.)  solutk>n  of  copper  sulphate 
in  water  becomes  coated  immediately  with  a  black 
or  brown  furry  coating  of  metallic  copper,  which 
continues  to  be  thrown  down  till  all  the  zinc  has 
dissolved.  A  few  small  bubbles  of  hydrogen 
sometimes  escape,  but  these  may  be  neglected,  as 
they  represent  only  an  extremely  minute  quantity 
of  zinc.  In  order  to  show  the  ratio  between  the 


Observation — Quantitative  19 

weight  of  zinc  dissolved  and  copper  deposited,  the 
clean  zinc  must  be  weighed  and  placed  in  a  small 
beaker  containing  the  solution  of  copper,  which 
must  be  used  in  excess — that  is,  it  must  remain 
blue  after  the  zinc  is  dissolved.  The  action  is  over 
when  on  feeling  about  with  a  glass  rod  no  particles 
of  the  zinc  are  encountered.  It  is  advisable  to 
warm  the  solution  toward  the  end.  The  reddish 
precipitate  of  copper  is  allowed  to  settle,  the 
blue  solution  containing  zinc  and  copper  sulphates 
poured  off,  and  the  precipitate  brushed  by  means  of 
a  camel-hair  brush  into  a  counterpoised  crucible. 
The  washing  is  completed  in  the  crucible,  by 
adding  some  boiling  water,  which,  after  settlement 
of  the  copper,  is  poured  off  as  completely  as 
possible.  As  the  pulverulent  metal  is  liable  to 
oxidise  if  heated  in  contact  with  the  air,  it  should 
be  dried  rapidly,  and  this  may  be  accomplished 
by  adding  to  it  a  few  cubic  centimetres  of  strong 
alcohol,  pouring  this  away,  and  then  placing  the 
crucible  in  a  steam  oven  for  a  few  minutes.  It  is 
weighed  when  cold.  Theoretically  I  gram  of  zinc 
precipitates  '97  gram  of  copper.  By  experiment 
conducted  in  the  manner  described,  '57  gram  of 
zinc  gave  -55  gram  copper,  which  is  in  the  propor- 
tion of  i  to  -965. 

By  a  similar  method  of  procedure  : 

I    gram    magnesium    precipitates    2*64    grams 

of  copper. 
i  gram  copper  precipitates  3  -40  grams  of  silver. 

C2 


2O     Teaching  of  Elementary  Chemistry 

i  gram  magnesium  precipitates  9  grams  of  silver 
I  gram  zinc  „       3-32      „      „      „ 

In  the  case  of  replacing  silver  by  copper  mag- 
nesium or  zinc,  an  excess  of  solution  of  silver  nitrate 
may  be  used* 

/From  results  obtained  in  this  way  the  Law 
of  Reciprocal  Proportions  or  Equivalents  may  be 
tested  by  the  .pupil  for  himself.  He  finds,  for 
example,  by  successive  experiments,  and  calcu- 
lating from  the  results,  that  I  part  of  magnesium, 
271  parts  of  zinc,  and  2*62  parts  of  copper  are 
respectively  required  to  precipitate  9  parts  of  silver. 
From  this  he  may  infer  that  2*71  parts  of  zinc  and 
2*62  parts  of  copper ;  are  equivalent  to  each  other, 
or  are  capable  of  doing  an  equal  amount  of  chemical 
work.  This  he  can  verify  by  recalculating  the 
result  of  his  experiment  in  which  copper  is  preci- 
pitated by  zinc,  for 

I   :  -97  ::  271    :    2*62. 

Similarly  he  may  infer  that  I  part  of  magnesium 
is  equivalent  to  271  parts  of  zinc,  though  this 
cannot  be  similarly  verified  by  direct  precipitation. 
In  a  later  chapter  an  experiment  will  be  described 
by  which  the  weight  of  hydrogen  corresponding 
to  these  quantities  of  the  metals  can  be  experi- 
mentally determined  ;  but  as  this  requires  more 
careful  manipulation,  and  the  observation  of 
weight  to  the  third  place  of  decimals,  it  is  not 
within  the  capacity  of  pupils  at  this  stage. 


CHAPTER   III 

OBSER  VA  TION-QUANTITA  TIVE 

Measurement  of  gases — In  the  preceding 
chapter  the  experiments  described  involve  deter- 
minations of  gain  or  loss  of  weight.  The  pupil 
may  now  proceed  to  make  estimations  of  the  volume 
of  gas  obtained  in  various  processes,  and  it  is  sur- 
prising what  clpse  approximations  to  theoretical 
results  are  possible  by  the  use  of  the  simplest 
apparatus  and  by  methods  which  appear  to  be 
among  the  least  exact.  Estimations  of  the  volume 
of  hydrogen  evolved  from  acids  by  various  metals 
afford  the  best  exercises  to  begin  upon,  and  at  first 
all  calculations  may  be  neglected,  inasmuch  as  the 
solubility  of  hydrogen  in  water  and  the  difference 
between  ordinary  atmospheric  conditions  and  nor- 
mal temperature  and  pressure  have  comparatively 
little  effect  on  the  volume  of  gas  collected.  The 
apparatus  shown  in  the  figure  may  be  recommended 
for  its  simplicity.  It  consists  of  a  piece  of  tubing 
about  20  cm.  long,  6-8  mm.  internal  diameter, 
drawn  out  at  the  top  and  bent  into  a  curve,  upon 


22     Teaching  of  Elementary  Chemistry 

which  is  fitted,  by  means  of  a  short  piece  of  rubber 
tubing,  a  second  piece  of  quill  glass  tubing,  turned 
up  at  the  end  so  as  to  convey  the  gas  into  a  jar. 
The  metal,  zinc  foil,  or  magnesium  ribbon  is 
thrust  into  the  wider  tube,  and,  to  prevent  portions 
of  it  from  falling  out  of  the  open  end,  a  little  plug 
of  copper  gauze  is  stuffed  into  the  mouth. 

To  collect  the  gas  a  common  stoneware  pneu- 
matic trough,  with  beehive  shelf  and  cylindrical  gas 


FIG.  4 

jar  filled  with  water,  may  be  used.  To  make  the 
experiment,  the  upturned  end  of  the  delivery  tube 
is  put  under  the  mouth  of  the  jar,  and  a  deep 
beaker  or  cylinder  containing  dilute  sulphuric  acid 
is  brought  under  the  tube  containing  the  metal, 
and  the  latter  is  slowly  lowered  into  it.  Evolution 
of  gas  commences  immediately,  and  the  gas  passes 
into  the  jar.  When  the  whole  of  the  metal  is  dis- 
solved, the  tube  may  be  removed  and  the  level  of 


Observation — Quantitative  2  3 

the  water  in  the  jar  is  marked  off  by  means  of  a 
strip  of  paper  label,  which  is  affixed  to  the  outside 
of  the  jar,  and  the  edge  of  which  marks  the  surface 
of  the  water  or  of  the  gas.  The  jar  may  then 
be  lifted  out  of  the  trough,  water  poured  into  it  till 
the  surface  is  level  with  the  edge  of  the  paper 
strip,  and  this  water,  which  now  occupies  the  space 
taken  up  previously  by  the  gas,  is  measured  by 
pouring  it  out  into  a  graduated  cylinder. 

No  attempt  should  be  made  to  expel  the  whole 
of  the  gas  from  the  tube  into  the  jar,  for  this 
residual  gas  occupies  the  space  previously  filled  by 
air,  which  at  the  beginning  of  the  experiment  was 
driven  into  the  jar.  When  magnesium  is  used  it 
should  be  lowered  into  the  acid  very  cautiously  or 
some  bubbles  of  gas  may  be  lost. 

A  series  of  experiments  should  in  the  first 
instance  be  made  as  described,  and  the  resulting 
volume  of  gas  recorded  in  the  notebook  ;  at  the 
same  time  the  temperature  of  the  water  and  the 
height  of  the  barometer  may  be  noted,  the  correc- 
tions being  reserved  by  beginners,  and  applied 
later,  when  they  have  learned  the  effect  of  changes 
of  temperature  and  pressure  upon  gases,  and  can 
make  the  necessary  calculations. 

One  gram  of  zinc  gives  theoretically  343  c.c. 
of  hydrogen  at  normal  temperature  and  pressure. 
An  experiment  in  which  *86  of  zinc  foil  was  used 
gave  3 1 5  c.c.  at  20°  ;  I  gram  would,  therefore,  have 
given  366  c.c.,  or  341  c.c.  at  normal  temperature.  - 


24     Teaching  of  Elementary  Chemistry 

One  gram  of  magnesium  gives,  theoretically, 
930  c.c.  of  hydrogen  at  normal  temperature  and 
pressure. 

By  experiment,  '38  gram  of  magnesium  gave 
385  c.c.  of  hydrogen  at  20°:  so  that  I  gram  would 
have  given  1013  c.c.,  or  943  c.c.  at  normal  tem- 
perature. 

Here  it  may  be  remarked  that  the  correction 
required  for  pressure  is  usually  much  less  than 
the  correction  for  temperature,  and  may  very 
commonly  be  neglected  altogether  for  purposes 
such  as  we  have  in  view  in  these  experi- 
ments. 

It  may  be  observed  that  the  measurement  of 
the  gas  evolved  from  acid  by  the  metals  may  be 
made  use  of  for  the  purpose  of  estimating  the 
quantities  of  aluminium,  zinc,  and  magnesium, 
which  are  equivalent  to  one  another,  by  calculat- 
ing from  the  result  obtained  the  amount  of  metal 
required  to  yield  the  same  amount,  say  1000 
c.c.,  of  hydrogen. 

Another  good  form  of  experiment  involving 
the  measurement  of  gas  is  the  estimation  of  oxygen 
in  atmospheric  air  by  means  of  phosphorus.  A 
graduated  measuring  cylinder  may  be  used  for  this 
purpose,  or  simply  a  plain  gas  cylinder  holding 
about  250  c.c.  A  scratch  is  made  about  5  cm. 
from  the  mouth,  and  the  capacity  of  the  jar  to  this 
mark  is  ascertained  by  filling  with  water  and 
measuring  the  water.  The  jar  is  then  inverted  in 


Observation— Quantitative  2  5 

a  water-trough,  and  the  air  admitted  till  the  sur- 
face of  the  water  inside  stands  at  the  mark.  The 
air  in  the  jar  then  occupies  the  bulk  of  the  measured 
quantity  of  water. 

A  piece  of  clean  phosphorus,  the  size  of  a  pea, 
is  now  stuck  at  the  end  of  a  piece  of  copper  wire, 
and  thrust  up  into  the  jar  till  it  is  near  the  top. 
The  whole  is  allowed  to  stand  6-8  hours,  the  phos- 
phorus withdrawn,  and  the  new  level  of  the  water 
marked  off  with  a  strip  of  gummed  paper.  The 
volume  of  the  residual  nitrogen  can  then  be 
measured  by  means  of  water  as  before. 

Measurement  of  liquids.  Neutralisation  of  acids 
and  alkalis. — The  metric  system  of  weights  and 
measures  is  a  subject  included  in  the  syllabus  of 
the  Science  and  Art  Department,  and  every  teacher 
who  professes  to  meet  the  requirements  of  the 
Department  will  find  it  necessary  to  give  occa- 
sional demonstrations  of  the  relations  between  the 
several  denominations  of  weight  and  measure. 
This  is  one  of  those  subjects  which  cannot  be 
acquired  offhand,  but  demands  repeated  consi- 
deration and  use  to  make  it  familiar.  Whether 
it  has  already  been  learned  or  not  by  the  pupils,  it 
will  be  advisable  at  this  stage  to  begin  operations 
by  allowing  them  to  handle  some  of  the  common 
measuring  vessels  of  different  forms,  and  to  note 
the  relation  of  burettes  to  graduated  cylinders, 
flasks,  &c.  Volumetric  exercises  in  great  variety 
may  then  be  practised. 


26     Teaching  of  Elementary  Chemistry 

For  the  purposes  now  contemplated  we  may 
assume,  without  appreciable  error,  that  fresh  oil  of 
vitriol,  which  has  not  been  long  exposed  to  the  air, 
may  be  regarded  as  consisting  of  real  sulphuric 
acid,  H2SO4.  This  assumption  will  be  convenient 
to  the  teacher,  though  it  is  unnecessary  and  un- 
desirable to  communicate  at  first  any  notions  of 
this  kind  to  the  pupil.  A  standard  solution  of 
dilute  sulphuric  acid  may  be  prepared  by  weighing 
out  49  grams  of  oil  of  vitriol  in  a  small  beaker, 
and  pouring  this  into  water,  sufficient  being  used, 
together  with  the  rinsings  of  the  beaker,  to  make 
up  1000  c.c. 

The  next  step  is  to  make  choice  of  indicators, 
and  it  will  be  found  that  litmus  or  cochineal 
is  the  most  useful.  The  burette  to  be  used  may 
be  divided  into  '2  or  *i  c.c.  With  the  aid  of  the 
solution  of  sulphuric  acid,  a  number  of  experi- 
ments may  be  quickly  made  on  the  neutralising 
power  of  various  common  alkaline  solutions,  such 
as  solution  of  potash,  soda,  or  ammonia,  or  of  solid 
alkaline  substances  such  as  sodium  carbonate. 
The  only  special  precaution  to  be  taken  in  dealing 
with  carbonates  is  that  when  litmus  is  used  the 
liquid  requires  to  be  boiled  in  order  to  effect  com- 
plete decomposition  and  expulsion  of  the  carbonic 
"acid.  Details  of  the  mode  of  operating  are  given 
in  so  many  manuals  that  it  is  unnecessary  to 
describe  the  common  process  of  alkalimetry  or 
acidimetry  in  this  place. 


UNIVERSITY; 

^  »ui*..  ^S 

27 

Suppose  now  it  is  found  that  50  c.c.  of  the  sul- 
phuric acid  are  required  to  neutralise 

a  c.c.  of  solution  of  potash 
b  c.c.  of  solution  of  soda 
or  c  grams  of  sodium  carbonate. 

We  can  apply  either  of  these  facts  to  ascertain 
the  neutralising  power  of  other  acids.  Thus  a  c.c. 
of  solution  of  potash  will  be  found  to  neutralise 

m  c.c.  of  hydrochloric  acid 
n  c.c.  of  nitric  acid 
or/  grams  of  oxalic  acid. 

Then  a,  b,  or  c  will  neutralise  not  only  50  c.c.  of 
•Sulphuric  acid,  but  m,  n,  or  /  of  the  other  acids, 
and  so  these  quantities,  a,  b,  c,  m,  n  /,  are  re- 
spectively equivalent  to  one  another.  So  important 
is  it  to  secure  due  and  exact  attention  to  fact 
before  permitting  the  introduction  of  theory,  that 
in  this  part  of  the  work  again  the  author  would 
impress  upon  teachers  once  more  the  advisability 
of  requiring  young  pupils  to  practise  the  obser- 
vations of  neutralising  power  before  they  are 
allowed  to  use  formulae.  When  the  mere  manipu- 
lation has  been  mastered,  the  explanation  may  be 
given  of  the  use  of  the  specific  quantity  of  sul- 
phuric acid  taken  for  the  preparation  of  the 
standard  solution,  and  the  reactions  may  be  ex- 
pressed by  equations.  It  will  be  well,  however, 
to  confirm  the  result  expressed  in  the  equation  in 


28     Teaching  of  Elementary  Chemistry 

a  few  cases  by  direct  experiment.  Thus  the 
amount  of  HC1  in  a  sample  of  hydrochloric  acid 
having  been  determined  volumetrically,  as  ex- 
plained above,  50  c.c.  of  the  liquid  may  be  exactly 
neutralised  by  soda,  and  the  solution  evaporated 
to  dryness  in  a  small  counterpoised  porcelain  dish 
heated  by  a  water  bath.  The  salt  when  dry  may 
be  weighed.  Another  more  difficult  process  would 
be  to  place  a  weighed  quantity  of  salt  in  a  small 
flask  connected  with  a  bulb  absorption  apparatus 
containing  distilled  water.  On  adding  excess  of 
strong  sulphuric  acid  to  the  salt  and  heating,  the 
whole  of  the  hydrochloric  acid  gas  may  be  driven 
into  the  water,  and  the  resulting  solution  tested 
volumetrically  by  alkaline  solution  of  known 
strength, 

For  exercise  in  manipulation  and  observation 
without  the  interference  of  theory  there  is  no 
better  example  than  the  application  of  the  soap 
test  to  the  estimation  of  '  hardness '  in  water.  It  is 
not  necessary  to  describe  this  process  here,  as  an 
account  of  it  is  to  be  found  in  nearly  all  books  on 
analysis.-  -  . 

The.  following  statement  occurred  in  a  paper 
sent  up  ;at  ithe  recent  May  examination  (1895) 
*  Common 'salt  is  called  sometimes  sodium  chloride, 
and  this  shows  that  it  must  contain  chlorine  by  the 
namei'  The  childish  character  of  such  an  answer 
may  be  thought  to  be  exceptional ;  but  though  it 
is  true  that  such  a!  crude  form  of  statement  is  not 


Observation — Quantitative  29 

common,  the  fact  remains  that  names  and  formulae 
are  often  used  as  expressions  of  fact  when  they  re-> 
present  the  thing  that  is  to  be  proved.  An  illus- 
tration of  this  is  almost  certain  to  occur  whenever 
the  examinees  are  requested  to  illustrate  the  law 
of  multiple  proportions  by  referring  to,  say,  the 
oxides  of  nitrogen.  The  formulae,  having  been 
committed  to  memory,  are  at  once  produced,  the 
candidates  being  apparently  unconscious  that  any 
reference  to  them  is  equivalent  to  begging  the 
whole  question.  If,  however,  the  problem  is  stated 
in  another  form  without  supplying  the  names  of 
the  elements  concerned,  students  seem  to  be  in- 
capable of  attacking  the  question,  and  it  remains 
usually  unanswered.  Suppose  the  question  to 
stand  as  follows  :  *  Two  elements  A  and  B  combine 
in  the  following  proportions  : 

A  B 

I       .       .       „       96:28 
II       .       .       .       92-83 

III  .          >"•.       .  89-62 

IV  86-62 


372  <'•  /<H? 

7-17 
10-38 
i3'38 


Show  that   these  combinations  comply  with  the 
law  of  multiple  proportions/ 

All  that  has  to  be  done  is  to  make  one  of  these, 
say  A,  a  fixed  quantity,  and  to  calculate  the  several 
proportions  of  the  second  element  which  are  com- 
bined with  this  quantity,  and  then  see  whether 
they  stand  in  the  simple  relation  to  one  another 
required  by  the  law.  If  in  the  above  example  we 
calculate  the  amount  of  B  which  is  in  each  com- 


3O     Teaching  of  Elementary  Chemistry 


pound  united  with  100  parts  of  A,  the  figures  stand 

as  follows : 

A 

I       .       .        ioo 

II        .        .        ioo 

III  ioo 


IV 


IOO 


B 

3-86 

772  or  3-86  x  2 
11-58  or  3-86  x  3 
15-45  or  3-86x4 

Q.E.D. 


CHAPTER    IV 

CHEMICAL   EQUIVALENTS-THE  LA\V    0* 
VOLUMES 

IN  the  last  chapter  experimental  methods  were 
described  by  which  the  volumes  of  hydrogen 
expelled  from  acids  by  the  action  of  several 
different  metals  could  be  estimated,  and  hence  the 
weight  of  the  metals  equivalent  to  one  another 
could  be  determined. 

It  is  important  for  the  foundation  of  chemical 
theory  to  be  able  to  substitute  the  mass  for  the 
volume  of  the  hydrogen  in  these  and  similar  cases, 
so  as  to  be  in  a  position  to  express  the  chemical 
equivalents  of  the  metals  in  terms  of  hydrogen 
taken  as  the  unit.  In  order  to  accomplish  this, 
we  must  know  the  weight  of  a  unit  volume  of 
hydrogen.  This  cannot  be  determined  directly 
by  any  experimental  process,  which  is  accurate 
enough  and  at  the  same  time  sufficiently  easy  to 
be  attempted  by  young  students.  But  an  equi- 
valent result  may  be  attained  by  making  use  of  a 
form  of  experiment  familiar  in  analytical  chemistry, 
in  which  the  loss  of  weight  consequent  upon  the 
escape  of  gas  from  a  light  glass  apparatus  is  deter- 


32     Teaching  of  Elementary  Chemistry 

mined.  A  plan  has  already  been  described  by 
which  the  hydrogen  expelled  from  an  acid  by  a 
weighed  quantity  of  metallic  magnesium  can  be 
collected  and  measured  ;  by  the  following  device 
the  weight  of  this  hydrogen  can  be  determined.1 

The   apparatus   consists    of    a    wide-mouthed 
weighing  bottle  of  thin  blown  glass.     Through  a 


FIG,  5 

rubber  stopper  pass  two  tubes  ;  one  as  shown  bent 
at  right  angles  and  'closed  by  a  light  rubber  cap ; 
the  other  shaped  as  shown  in  the  figure,  the  bulb 
being  filled  with  loose  fibrous  asbestos.  About 

1  The  suggestion  that  this  can  be  accomplished  was  derived  from 
Professor  J.  Emerson  Reynolds's  *  Experimental  Chemistry  for 
Junior  Students'  (Longmans),  a  book  which  deserves  the  attention 
of  all  teachers. 


Chemical  Equivalents  33 

5  c.c.  of  water  are  placed  in  the  bottle,  together 
with  the  weighed  quantity  of  metal.  The  bulb 
tube  is  dipped  into  a  beaker  of  strong  sulphuric 
acid  till  the  lower  part  is  rilled,  as  shown  in  the 
sketch.  The  outside  of  this  tube  is  then  washed 
free  from  sulphuric  acid,  and  the  stopper  bearing 
the  tube  fixed  in  its  place.  The  whole  apparatus 
is  then  placed  on  the  pan  of  the  balance,  and 
weighed  carefully,  the  weight  being  noted  to  milli- 
grams. The  whole  apparatus  should  not  weigh 
more  than  30  to  40  grams.  The  weight  having 
been  recorded,  a  small  piece  of  rubber  tubing  is 
attached  to  the  open  end  of  the  bulb  tube,  and  by 
blowing  gently  a  few  drops  of  sulphuric  acid  may 
be  expelled  into  the  water,  in  which  the  metal 
is  immersed.  Hydrogen  is  immediately  evolved, 
and,  escaping  through  the  tube  containing  the  oil 
of  vitriol,  is  dried  in  its  exit  When  the  whole  of 
the  metal  has  been  dissolved,  the  cap  is  removed 
from  the  end  of  the  right-angled  tube,  and  air  is 
gently  sucked  through  the  rubber  attached  to  the 
bulb  tube.  The  residual  hydrogen  is  thus  replaced 
by  air,  and,  after  a  few  minutes,  the  apparatus  is 
ready  to  be  weighed. 

The  following  are   the   results  of  an  experi- 
ment: 

Magnesium  taken     , . -.•         /       .,       ,»         .  "12  gr. 

Weight  of  apparatus  before  solution  of  metal,   34*469  gr. 

»  „         after  „  „      34-459  gr. 

Loss  of  weight       *oio  gr. 
D 


34     Teaching  of  Elementary  Chemistry 

Thus  magnesium  expels  from  dilute  acid  -j1^  of  its 
weight  of  hydrogen,  or  12  parts  of  magnesium 
replace  I  part  by  weight  of  hydrogen.  Now, 
having  shown  by  previous  experiments  that  I  gram 
of  magnesium  produces  from  dilute  sulphuric  acid 
about  930  c.c.  of  hydrogen  and  TV  of  a  gram 
is  "0833,  this  is  the  weight  of  930  c.c.  of  the  gas : 
1000  c.c.  of  hydrogen  would,  therefore,  weigh  '0895, 
which  is  near  enough  to  the  figure  usually  given, 
viz.  "0896  gram. 

The  determination  of  the  composition  of  water 
by  weight  is  another  experiment  of  the  same  order 
which  may  be  done  by  pupils  at  about  the  same 
stage. 

For  this  experiment  we  require  a  Kipp  or 
other  apparatus  for  generating  a  stream  of  hydrogen 
free  from  air,  a  couple  of  tubes  containing  pumice 
stone  wetted  with  strong  sulphuric  acid  in  order 
to  dry  the  gas,  a  tube  containing  pure  dry  oxide 
of  copper  which  can  be  weighed,  and  an  apparatus 
also  light  enough  to  be  weighed,  in  which  the 
water  formed  can  be  collected.  The  shape  of  a 
convenient  apparatus  for  gathering  the  whole  of 
the  water  without  loss  by  vaporisation  is  shown 
in  fig.  6,  where  a  represents  one  of  the  tubes  by 
which  the  stream  of  hydrogen  is  rendered  dry ;  b 
is  a  bulb  tube  of  hard  glass  containing  pure  dry 
black  oxide  of  copper ;  the  end  of  this  tube  is 
turned  down  at  a  right  angle,  and  the  extremity 
cut  off  obliquely.  This  tube  is  suspended  by  means 


Chemical  Equivalents 


35 


of  a  thin  piece  of  iron  or,  better,  platinum  wire 
from  any  suitable  support,  and  by  the  same  wire 
it  can  be  attached  to  the  beam  of  the  balance 
when  it  has  to  be  weighed.  The  thistle  funnel 
has  a  bulb  on  the  stem,  the  lower  end  of  which 
dips  through  a  cork  into  some  oil  of  vitriol  con- 
tained in  a  short  test-tube.  There  is  a  short  exit 


FIG.  6 


tube  from  the  cork  for  the  escape  of  the  excess  of 
hydrogen.  The  whole  of  c  can  be  hung  on  the 
balance  by  means  of  a  wire  loop.  For  the  success  of 
the  experiment,  the  copper  oxide  should  be  freshly 
ignited,  so  as  to  ensure  its  dryness  and  freedom 
from  nitrate  or  other  impurity,  and  the  stream  of 
hydrogen  should  be  carried  through  the  whole  series 
of  tubes  at  a  moderate  speed  for  5  to  10  minutes 


36     Teaching  of  Elementary  Chemistry 

before  the  copper  oxide  is  heated,  b  and  c  are  to 
be  weighed  as  accurately  as  possible  at  the 
temperature  of  the  air  before  and  after  the  reduc- 
tion of  the  oxide  and  formation  of  the  water.  The 
gain  of  weight  in  c  (water)  should  be  to  the  loss 
of  weight  in  b  (oxygen)  in  the  ratio  of  9  to  8. 

The  fact  that  oxygen  combines  with  twice 
its  volume  of  hydrogen  was  observed  by  Cavendish 
in  the  middle  of  the  last  century,  but  it  was  Gay- 
Lussac !  who  established  the  generality  of  the  prin- 
ciple that  gaseous  combinations  are  formed  by  the 
union  of  their  constituents  in  very  simple  volumetric 
proportions.  Thus  he  observed  that 

100  vols.  of  oxygen  combine  with  200  vols.  of 
hydrogen. 

100  vols.  of  muriatic  acid  combine  with  100  vols. 
of  ammonia. 

100  vols.  of  carbon  dioxide  combine  with  200 
vols.  of  ammonia. 

He  also  drew  attention  to  the  established  com- 
position of  ammonia,  which  consists  of  100  vols.  of 
nitrogen  to  300  vols.  of  hydrogen  ;  the  composition 
of  sulphuric  anhydride,  which  is  formed  of  100  vols. 
of  sulphur  dioxide  united  to  50  vols.  of  oxygen  ; 
of  carbonic  anhydride,  which  is  composed  of  100  vols. 
of  carbonic  oxide  and  5°  vols.  of  oxygen,  and  to 
the  composition  of  the  oxides  of  nitrogen.  From 
all  these  facts  Gay-Lussac  drew  conclusions  which 
supplied  very  important  arguments  in  favour  of 

1  See  «  Alembic  Club  Reprints,'  No.  4,  p.  15, 


Chemical  Equivalents  37 

Dalton's  Atomic  Theory,  at  that  time  still  under 
discussion,  and  far  from  being  the  generally  accepted 
basis  of  chemical  theory  it  is  at  the  present  day. 

The  experimental  demonstration  of  the  volu- 
metric composition  of  hydrogen  chloride,  water,  and 
ammonia  is  a  matter  of  fundamental  importance, 
but  is  best  exhibited  by  the  more  experienced  hand 
of  the  teacher.  The  methods  generally  in  use  for 
this  purpose  were  for  the  most  part  devised  by 
Hofmann,  whose  '  Introduction  to  Modern  Chemis- 
try,' though  published  a  quarter  of  a  century  ago, 
is  still  delightful  and  instructive  reading.  As  all 
these  processes  are  described  in  the  principal  text- 
books, and  particularly  in  detail  in  Mr.  Newth's 
•'  Chemical  Lecture  Experiments '  (Longmans),  it  is 
unnecessary  to  repeat  the  account  of  them  in  this 
place.  One  or  two  remarks,  however,  are  neces- 
sary to  indicate  what  each  experiment  serves  to 
establish. 

Hydrogen  chloride. — It  is  usual  to  analyse 
hydrogen  chloride  gas  by  means  of  sodium 
amalgam.  It  must,  however,  be  noted  that  this 
experiment  merely  proves  that  2  vols.  of  the  gas 
contain  I  vol.  of  hydrogen  ;  it  gives  no  information 
as  to  the  volume  of  the  chlorine  with  which  this 
I  vol.  of  hydrogen  is  united. 

The  volume  of  the  chlorine  can  only  be  shown 
by  collecting  the  gas  which  results  from  electrolysis 
of  the  strong  aqueous  solution,  and  showing  that  it 
contains  half  its  volume  of  chlorine  and  half  its 


38     Teaching  of  Elementary  Chemistry 

volume  of  hydrogen.  The  absorption  of  the 
chlorine  from  the  mixed  gas  is  best  effected  by 
means  of  concentrated  solution  of  potassium  iodide. 
Not  only  is  half  the  gas  absorbed,  but  the  liberated 
iodine  serves  to  demonstrate  the  nature  of  the 
gas. 

Water. — As  to  the  composition  of  water,  it  must 
be  observed  that  the  process  of  electrolysis  so  com- 
monly resorted  to  proves  only  the  ratio  of  the 
hydrogen  to  the  oxygen,  and  is  therefore  incomplete 
as  a  demonstration  of  the  composition  of  water. 
To  show  the  volumetric  relation  of  water  gas  to  its 
constituents,  the  process  must  be  synthetical  — that  is, 
the  method  must  be  used  which  consists  in  uniting 
2  vols.  of  hydrogen  with  I  vol.  of  oxygen  at  a  tem- 
perature above  100°  C. 

Ammonia. — The  ratio  of  the  volume  of  hydrogen 
to  that  of  nitrogen  in  ammonia  is  shown  by  the 
chlorine  process ;  but  the  proof  that  3  vols.  ot 
hydrogen  and  I  vol.  of  nitrogen  are  contained  in 
2  vols.  of  ammonia  is  obtained  only  by  decompos- 
ing a  measured  quantity  of  ammonia  by  heat,  and 
subsequently  analysing  the  resulting  mixture  of 
hydrogen  and  nitrogen.  This  is  usually  accom- 
plished by  sparking  the  gas  till  its  volume  is  doubled, 
and  then  heating  in  the  mixed  gas  a  particle  of 
cupric  oxide,  which  converts  the  hydrogen  into 
water. 

The  composition  of  ammonia  cannot  be  con- 
veniently demonstrated  by  exploding  the  gas  with 


Chemical  Equivalents  39 

oxygen  ;  for  combustion  with  excess  of  oxygen 
leads  to  the  production  of  so  considerable  a 
quantity  of  oxides  of  nitrogen  as  to  render  the 
process  worthless  for  analytical  purposes. 

From  the  experiments  just  referred  to  we  learn 
that  equal  volumes  of  chlorine,  oxygen,  and  nitro- 
gen combine  respectively  with  one,  two,  and  three 
volumes  of  hydrogen.  Hence,  without  any  assump- 
tions as  to  atoms  or  molecules,  we  may  express  the 
composition  of  these  gases  by  the  formulae  HC1, 
H2O,  H3N,  in  which  the  symbols  H,  Cl,  O,  N  re- 
present unit  volumes  of  the  constituents. 

We  know  also  that  sodium  and  other  metals 
acting  upon  these  gases  expel  from  them  part  of 
the  hydrogen  they  contain,  and  take  the  place  of 
the  hydrogen  so  removed,  the  amount  of  hydrogen 
replaced  being  one-half  in  the  case  of  water,  and 
one-third  in  the  case  of  ammonia,  while  from 
hydrogen  chloride  the  whole  of  the  hydrogen  is 
removed  at  once.  These  facts  are  recorded  in  the 
formulae. 

In  the  earlier  chapters  great  stress  was  laid  upon 
the  importance  of  cultivating  the  powers  of  observa- 
tion ;  but,  to  make  any  progress  with  the  theory 
of  chemistry,  it  is  equally  necessary  to  practise  the 
careful  consideration  and  selection  of  evidence,  and 
to  form  habits  of  reasoning  thoughtfully  from  facts 
previously  established.  The  confusion  so  often 
existing  in  the  minds  of  students  is,  in  general,  due 
partly  to  the  use  of  unfamiliar  language,  partly  to 


4.O     Teaching  of  Elementary  Chemistry 

want  of  experience  in  observation  and  in  reasoning. 
This  want  of  experience  of  phenomena  and  of  the 
nature  of  scientific  evidence  renders  the  condition 
of  the  student-mind  quite  comparable  with  that  of 
the  early  investigators.  Some  knowledge  of  the 
history  of  the  development  of  modern  chemistry 
from  the  time  of  Boyle  onwards  is  therefore  very 
valuable  to  the  teacher.  Frequent  reference  to  a 
good  English  dictionary  even  by  the  teacher  is 
also  a  practice  which  cannot  be  too  strongly  com- 
mended. The  statement  by  a  pupil  that  'metals 
are  hard  and  brittle,  and  are  also  malleable  and, 
ductile/  is  a  proof  that  the  wholesome  custom  of 
explaining  the  meaning  of  words  must  have  been 
neglected  by  that  boy's  teacher.  Endless  examples 
of  the  same  defects  are  noticeable  not  only  in  the 
papers  sent  in  by  candidates  at  the  examinations 
of  the  Science  and  Art  Department,  but  at  the 
Matriculation  of  the  London  University  and  other 
examinations  of  junior  students  within  the  experi- 
ence of  the  author. 

In  the  matter  of  selecting  evidence  great  mis- 
takes are  commonly  made,  in  many  cases  arising 
from  mere  indolent  habit  of  mind  or  positive 
inability  to  think.  A  question  recently  set  requir- 
ing evidence  of  the  presence  of  oxygen  in  nitrous 
and  nitric  oxides  was  generally  answered  by  the 
statement  that  '  they  support  combustion,  therefore 
they  contain  oxygen/  Here  *  support  combustion' 
may  be  assumed  to  refer  to  the  combustion  of  a 


Chemical  Equivalents  41 

candle.  In  the  first  place,  therefore,  it  is  not 
true  that  they  both  support  combustion  ;  but  this 
answer  also  ignores  the  fact  that  there  are  many 
known  examples  of  burning  where  there  is  no 
oxygen.  The  proof  required  is  as  follows  :  Pass 
the  gas  over  heated  copper,  then  subject  the  hot 
copper  oxide  to  a  stream  of  hydrogen,  and  show 
the  production  of  water.  To  make  the  proof  com- 
plete, a  knowledge  of  the  composition  ^f  water 
must  be  assumed,  and  the  water  must  be  fully 
identified  by  observation  of  its  physical  as  well  as 
chemical  characters. 

A  similar  case  occurs  in  the  comparison  of  the 
gas  obtained  from  chalk  by  heat  or  acids  with  that 
which  is  produced  by  combustion  of  charcoal,  by 
fermentation  of  sugar  or  in  animal  respiration.  It 
is  not  sufficient  to  point  to  the  white  precipitate 
with  lime  water  as  evidence  of  identity.  The/r0- 
bability  that  they  are  the  same  is  increased  by 
each  additional  character*— taste  and  odour,  solu- 
bility, density,  chemical  character — which  is  found 
to  be  alike  in  both,  "but  certainty  is  not  attained  till 
all  available  characters  have  been  examined 

It  may  not  be  within  the  power  of  young  stu- 
dents to  make  an  exhaustive  investigation  of  this 
kind,  but  the  teacher  should  be  careful  to  show  that 
there  are  different  stages  or  degrees  of  probability 
leading  up  to  proof. 


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H  -r 


44     Teaching  of  Elementary  Chemistry 

Note  to  Chapter  IV. 

The  preceding  chronological  table  was  drawn 
up  by  the  author  some  years  ago,  and  it  has  Been 
found  very  useful  in  his  own  teaching.  It  supplies 
the  names  of  those  chemists  of  the  past  who  may 
be  regarded  as  founders  of  modern  chemistry, 
when  they  lived,  and  the  length  of  each  life,  so  as 
to  show  at  a  glance  who  were  contemporary  at  any 
period.  The  table  only  includes  the  names  of 
deceased  chemists  who  have  substantially  ad- 
vanced the  theory  of  chemistry  by  their  discoveries 
or  by  their  writings.  A  crowd  of  well-known 
names  has  necessarily  been  omitted,  as  represent- 
ing contributors  to  the  detail  rather  than  to  the 
fundamental  principles  of  the  science,  and  in  a  few 
cases  it  may  be  .a  question  whether  the  names  in 
the  list  are  all  entitled  to  a  place  there.  Klaproth, 
for  example,  did  a  great  deal  of  work  relating  to 
the  details  of  mineral  analysis,  and  his  name  is 
admitted,  chiefly  on  the  ground  that  improve- 
ments in  the  art  of  analysis  lent  important  aid 
to  the  progress  of  the  science. 

A  general  survey  of  the  work  of  the  majority 
of  the  chemists  whose  names  appear  in  the  table 
is  provided  in  a  compact  form  in  Mr.  Pattison 
Muir's  volume  entitled  'Heroes  of  Science — 
Chemists'  (Society  for  Promoting  Christian  Know- 
ledge, 1883). 

There  is  also  Watts's  translation  of  the  *  History 


Chemical  Equivalents  45 

of  Chemical  Theory,'  by  the  late  Professor  Wurtz 
(Macmillan),  which  brings  the  story  down  to  1869, 
now  more  than  a  quarter  of  a  century  ago. 

Dr.  Thorpe's  charming  volume  of  '  Essays  in 
Historical  Chemistry  '  (Macmillan)  gives  a  critical 
review  of  the  work  and  an  account  of  the  life  of 
many,  but  not  all,  of  these  founders  of  Chemical 
Science. 


46 


CHAPTER  V 

MOLECULAR   WEIGHTS  AND   FORMULA 

THE  establishment  of  Gay-Lussac's  *  Law  of 
Volumes'  was  destined  to  lead  to  consequences 
of  the  utmost  importance  for  theoretical  chemistry. 
In  1811  Avogadro  published  his  discussion1  of 
the  constitution  of  gases  upon  the  basis  of  Gay- 
Lussac's  law,  and  although  it  attracted  compara- 
tively little  notice  at  the  time,  what  is  now  known 
as  the  law  of  Avogadro  became  half  a  century 
later  the  foundation  of  the  modern  system  of 
molecular  and  atomic  weights.  The  law  of 
Avogadro  states  that  equal  volumes  of  different 
gases  under  the  same  conditions  of  temperature 
and  pressure  contain  the  same  number  of  mole- 
cules. This  statement  is  sometimes  altered  by 
students,  and  even  by  teachers,  into  '  gaseous 
molecules  have  the  same  or  equal  volumes.'  This' 
is  wrong,  because  we  know  next  to  nothing  about 
the  dimensions  of  single  molecules ,:  all  that  we  can 

1  *  Essay  on  a  Manner  of  Determining  the  relative  Masses  of  the 
Elementary  Molecules  of  Bodies  and  the  Proportions  in  which  they 
enter  into  these  Compounds.'  See  *  Alembic  Club  Reprints,'  No.  4, 
p.  28. 


Molecular  Weights  and  Formula      47 

say  is  that  molecules  of  all  gases  require  on  the 
average  equal  spaces  to  move  about  in. 

The  density  of  a  gas  or  vapour  is  the  mass 
of  unit  volume,  taking  some  gas,  preferably  the 
lightest  of  all,  as  the  standard.  So  that  when  we 
say  the  density  of  oxygen  is  16,  of  nitrogen  14,  of 
carbonic  anhydride  22,  and  so  on,  we  mean  that 
equal  volumes  of  these  gases  weigh  16,  14,  22,  &c. 
units  when  the  weight  of  the  same  volume  of 
hydrogen  is  I  unit.  Now  it  can  be  shown  that 
the  molecule  of  hydrogen  is  divisible  into  two 
equal  parts.  The  hypothesis  of  the  divisibility 
of  many  molecules  is  discussed  very  clearly  in 
Avogadro's  essay,  to  which  reference  has  been 
made.  The  argument  may  run  in  this  way : 
Equal  volumes  of  hydrogen  and  chlorine  interact 
to  form  hydrogen  chloride,  the  volume  of  which 
is  equal  to  the  volume  of  the  hydrogen  added  to 
that  of  the  chlorine.  If  Avogadro's  hypothesis  is 
true,  as  we  assume  it  to  be,  this  process  may  be 
expressed  by  saying  that  a  molecule  of  hydrogen 
reacting  with  a  molecule  of  chlorine  gives  two 
molecules  of  hydrogen  chloride.  Hence  each 
molecule  of  hydrogen  chloride  must  contain  half 
the  hydrogen  contained  in  a  molecule  of  hydrogen, 
and  half  the  chlorine  contained  in  a  molecule  of 
that  gas.  Hence  the  molecules  of  hydrogen  and 
of  chlorine  are  respectively  divisible  into  two  equal 
parts,  and  the  molecular  weight  of  either  gas  may 
be  conveniently  taken  to  be  the  weight  of  two  unit 


48     Teaching  of  Elementary  Chemistry 

volumes.  The  determination  of  the  density  of  a  gas 
or  vapour,  therefore,  leads  directly  to  the  molecular 
weight  of  the  gas,  whether  elementary  or  compound. 
The  experimental  methods  of  determining  the 
densities  of  gases  used  by  such  great  experimenters 
as  Regnault  and  Lord  Rayleigh  are  exceedingly 
simple  in  principle  ;  but  attainment  to  great  ac- 
curacy requires  much  skill  and  experience,  and 
attention  to  many  details.  But,  though  the  method 
cannot  be  applied  by  beginners  to  the  case  of 
hydrogen  and  the  lighter  gases,  it  may  be  used  even 
by  young  students  with  considerable  success  when 


FIG.  7 

the  density  of  the  gas  is  so  great  that  the  experi- 
mental errors  of  weighing  and  those  due  to  impurity 
in  the  gas  stand  in  small  proportion  relatively  to 
the  whole  mass  to  be  weighed. 

Two  globes  are  taken  of  the  form  shown  in  the 
figure.  They  may  be  purchased  in  the  shape  of 
large  light  pipettes,  the  stems  of  which  may  be 
cut  off  four  or  five  cm.  from  the  globe  and  fitted 
with  light  rubber  caps.  The  globes  should  be  so 
chosen  as  to  be  as  nearly  as  possible  of  the  same 
capacity — viz.  250  to  300  c.c.  They  should  be  hung 
by  thin  wires  at  the  opposite  ends  of  the  beam  of 


OF  THE 

NIVERSITY 


Molecular  Weights  and  Formula      49 

the  balance  without  removing  the  pans,  and  the 
lighter  one  supplemented  by  a  small  piece  of 
glass  tubing  filed  down  so  as  to  supply  an  exact 
counterpoise.  One  of  the  globes  which  is  to  hold 
the  gas  must  have  its  capacity  determined  once  for 
all  by  filling  with  water  and  running  it  out  into  a 
measuring  vessel.  The  globe  is  then  dried  and 
filled  with  the  gas  by  displacement  of  air,  the  globe 
being  held  with  the  ends  vertical,  while  the  gas, 
if  heavier  than  air,  is  admitted  below. 

The  ends  of  the  tubes  are  then  closed  again 
with  the  caps.  On  replacing  the  globe  upon  the 
balance,  weights  will  have  to  be  added  to  the 
opposite  pan  to  restore  equilibrium.  These  weights 
cannot  be  taken  as  a  measure  of  the  mass  of  the 
gas,  as  in  the  case  of  solids  or  liquids,  inasmuch 
as  the  volume  of  air  displaced,  by  the  gas  in  this 
case,  has  an  effect  too  great  to  be  ignored.  The 
weight  of  this  displaced  air  must  be  calculated  and 
added  to  the  weights  used  in  order  to  arrive  at  the 
weight  of  the  gas  in  the  globe.  The  details  of  an 
experiment  will  make  the  matter  clear  : 

Capacity  of  globe  235  c.c. 

Weight  of  i  c.c.  of  air  at  normal  temperature 
and  pressure  =  '001293  7  gram.  At  17°,  the  tem- 
perature of  the  laboratory,  the  weight  of  I  c.c.  of 
air  is  '00122  very  nearly.  235  c.c.  therefore  weigh 
•286  gram.  Globe  filled  with  carbon  dioxide  re- 
quired for  counterpoise  '13  gram.  Then  '286  4-  "13 
—  •416  is  the  weight  of  235  c.c.  of  the  gas. 

E 


5O     Teaching  of  Elementary  Chemistry 


The  density  is  therefore    -—  =  r^$. 

"2oO 

Calculated  density  1*52  (air=i). 

The  determination  of  the  vapour  density  of 
various  volatile  solids  or  liquids  can  be  so  easily 
accomplished  by  Victor  Meyer's  air-expulsion  me- 
thod, and  the  calculations  involved  are  so  simple, 
that  even  young  students  may  successfully  practise 
the  operation.  It  is  not  necessary  to  give  an  ac- 
count of  the  process  in  this  place,  as  it  is  described 
with  full  detail  in  many  text-books.  Ether  (b.p.  35°) 
and  chloroform  (b.p.  61°)  may  be  used  as  examples 
of  substances  which  volatilise  readily  and  com- 
pletely in  boiling  water  ;  alcohol  (b.p.  78°)  and 
benzene  (b.p.  81°)  do  not  give  results  so  good, 
unless  the  water  is  saturated  with  common  salt, 
which  brings  up  the  boiling  point  to  110°.  The 
employment  of  higher  temperatures  requires  rather 
more  skill  than  beginners  usually  possess,  but  a 
bath  of  glycerine  or  oil,  or  any  of  the  organic 
liquids  of  constant  boiling  point  mentioned  in  the 
books,  may  be  used  when  the  pupil  has  had 
sufficient  practice. 

A  knowledge  of  molecular  weights  provides  one 
very  important  method  by  which  atomic  weights 
may  be  chosen.  The  atomic  theory  explains 
chemical  phenomena  by  the  assumption  that  com- 
bination results  from  the  close  approximation  and 
connection  of  minute  masses  of  elementary  matter 
called  '  atoms/  because  they  are  believed  to  be 


Molecular  Weights  and  Formula      51 

indivisible  by  the  forces  which  operate  in  chemical 
changes.  Chemical  decomposition  in  like  manner 
is  the  result  of  the  separation  of  the  atoms  forming 
a  compound  and  their  rearrangement  into  new 
combinations.  The  hypothesis  of  atoms,  however 
it  may  have  originated  and  developed  in  Dalton's 
mind,1  is  firmly  established  by  the  facts  which  are 
embodied  in  the  so-called  laws  of  chemical  com- 
bination. It  is  a  fact  that  (i)  elements  unite  in 
definite  proportions ;  that  (2),  if  two  elements 
combine  in  several  proportions,  these  proportions 
bear  a  simple  relation  to  one  another  ;  that  (3),  if 
two  elements  combine  with  a  third,  the  proportions 
in  which  they  unite  with  this  third  element  are  the 
same  proportions  or  simple  multiples  of  the  same 
proportions  in  which  they  combine  together,  should 
combination  between  them  ever  occur ;  and.  lastly, 
that  (4)  when  gases  unite  together,  the  volumes  so 
uniting  are  represented  by  very  simple  proportions. 
If  now  we  accept  the  doctrine  of  Avogadro,  the 
molecular  weight  is  proportional  to  the  specific 
gravity  of  the  substance  in  vapour.  For  example, 
the  molecule  of  carbon  dioxide  is  22  times  heavier 
than  the  molecule  of  hydrogen,  since  their  specific 
gravities  are  22  *  I. 

But   for   reasons    already   given,   the  molecule  of 
hydrogen  is  believed  to  be  divisible  into  two  equal 

1  There  seems  to  be  some  conflict  of  evidence  on  this  point. 
See  '  Life  of  Dalton,'  by  Sir  H.  E.  Roscoe,  '  Century  '  Series  ;  also 
*  A  New  View  of  ihe  Origin  of  Dalton's  Atomic  Theory,'  by  H.  E. 
Roscoe  and  A  Harden. 

£2 


52     Teaching  of  Elementary  Chemistry 

parts,  or,  in  other  words,  consists  of  two  atoms. 
Hence,  to  avoid  fractions,  the  relative  molecular 
weights  are  represented  as 

44:  2. 

Taking  two  volumes  of  hydrogen  as  the  standard 
volume  for  comparison  of  molecular  quantities  of 
all  gases,  we  have  a  means  of  fixing  atomic  weights. 
For  since  by  hypothesis  the  atom  of  an  element 
is  an  indivisible  quantity,  it  is  evident  that,  if  we 
measure  off  molecular  proportions  of  all  known 
.volatile  compounds  containing  that  element,  the 
smallest  quantity  of  the  element  in  question  ever 
observed  in  such  molecular  proportion  must  be 
assumed  to  be  one  atom,  until  and  unless  some 
other  compound  is  afterwards  found  containing  a 
smaller  quantity.  This  may  be  illustrated  by  the 
case  of  oxygen,  as  shown  in  the  following  table : 


Vapour 
density,  or 

Weight  of 

Weight  of 

weight  of 
i  volume 
of  vapour 

2  volumes 
of  vapour 

oxygen  in 
2  volumes 
of  vapour 

Water 

9 

18 

16 

Carbonic  oxide    . 

14 

28 

16 

Carbonic  anhydride 

22 

44 

32 

Nitrous  oxide 

22 

44 

16 

Nitric  oxide 

15 

30 

16 

Sulphurous  anhydride 

32 

64 

32 

Sulphuric  anhydride 

40 

80 

48 

Alcohol 

23 

46 

16 

Aldehyd      . 

22 

44 

16 

Acetic  acid 

30 

60 

32 

As   the  smallest   proportion   of  oxygen   ever 


Molecular  Weights  and  Formula      53 

found  in  two  volumes  of  the  vapour  of  any  of  its 
compounds  is  16  units  of  weight,  16  is  the  value 
assigned  to  the  atomic  weight. 

One  word  of  caution  is  necessary  in  conse- 
quence of  the  confusion  of  phraseology  still  pre- 
valent, even  in  the  writings  of  chemical  experts, 
in  reference  to  atomic  weights.  In  some  of  the 
principal  chemical  periodicals  we  find  papers  the 
titles  of  which  announce  that  they  refer  to  the 
*  atomic  weights '  of  various  elements,  as,  for 
example,  in  recent  years  the  atomic  weight  of 
oxygen,  of  chromium,  of  titanium,  of  silicon,  of 
tellurium,  &c.  In  nearly  all  these  cases  the 
inquiry  relates  not  to  the  determination  of  the 
atomic  weight,  but  of  the  combining  proportion  or 
equivalent  of  the  element  in  question.  In  fact,  it 
may  be  stated  as  a  general  rule  that  two  distinct 
operations  are  required  for  the  determination  of  the 
exact  value  of  the  atomic  weight  of  any  element, 
and  that  the  second  of  these  is  commonly  assumed 
or  ignored.  First,  the  combining  ratio,  or  equi- 
valent, is  determined  with  the  utmost  possible 
accuracy  by  the  analysis  or  synthesis  of  some  one 
or  more  of  its  compounds  ;  and,  secondly,  the 
equivalent  is  converted  into  the  atomic  weight  by 
multiplying  this  experimental  number  by  some 
factor — i,  2,  3,  4,  or  more — which  is  chosen  by 
appeal  to  some  other  wholly  different  criterion,  such 
as  that  just  referred  to  in  the  case  of  oxygen.  The 
atomic  weight  of  oxygen,  in  fact,  is  not  16  exactly 


54     Teaching  of  Elementary  Chemistry 

but  some  number  closely  approaching  16  which 
is  determined  by  analysis  of  water  and  other 
oxides. 

Other  examples  and  other  methods  are  given 
in  the  next  chapter. 


55 


CHAPTER  VI 

ATOMIC  WEIGHTS— CLASSIFICATION 

THE  calculation  of  the  atomic  weight  of  an  element 
must  in  all  cases  be  preceded  by  the  determination 
of  the  quantity  of  that  element  which  combines 
with  or  replaces  one  unit  weight  of  hydrogen. 
This  is  the  equivalent.  The  operations  which 
follow  are  of  different  kinds,  according  to  the 
character  of  the  element  concerned,  the  most 
important  being  the  following : 

I.  The  vapour  density  method,  described  in  the 
last  chapter.     It  is  a  mistake  to  assume,  as  is  some- 
times done,  that  the  vapour  densities  of  the  elements 
themselves  serve  as  a  guide  to  their  atomic  weights  ; 
for  though  it  is  true  that  the  vapour  densities  and 
atomic  weights  are  identical  in  a  few  cases,  this 
affords  no  evidence  towards  the  establishment  of 
the  atomic  weight  without  additional  information, 
and   beside   these   are  nearly  as  many  other  ele- 
ments (Hg,  Zn,  Cd,  As,  P)  whose  vapour  densities 
do  not  coincide  with  their  atomic  weights. 

II.  Appeal   to  the  Law  of  Dulong  and  Petit 


56     Teaching  of  Elementary  Chemistry 

relating  to  Specific  Heat.  Care  is  necessary  in 
expressing  this  law  ;  it  relates  only  to  the  elements 
in  the  solid  state,  and  does  not  hold  under  ordinary 
conditions  for  the  solids,  boron,  carbon,  silicon,  and 
beryllium. 

The  law  may  be  stated  in  various  ways  :  The 
specific  heat  of  a  solid  element  (with  the  named 
exceptions)  is  inversely  as  the  atomic  weight  ;  or, 
the  specific  heat  multiplied  by  the  atomic  weight 
is  a  constant  (about  6*4)  ;  or  the  atomic  weight  is 
the  quotient  obtained  by  dividing  6*4  by  the  specific 
heat. 

The  application  of  the  law  consists  in  finding 
what  multiple  of  the  equivalent  must  be  taken  to 
comply  with  the  formula 

n  Equiv.  x  Sp.  H.  =  6*4  (approx.), 

the  problem  being  to  find  the  value  of  n.  Now  n 
must  always  be  a  whole  number,  because  the 
atomic  weight  must  always  be  identical  with  the 
equivalent  or  some  multiple  of  it,  according  to 
the  valency  of  the  element.  The  atomic  weight 
obviously  cannot  be  deduced  directly  from  the 
value  of  the  specific  heat,  because  no  process  is 
known  by  which  the  specific  heat  can  be  deter- 
mined with  the  same  degree  of  accuracy  as  the 
equivalent.  This  should  be  explained  carefully, 
for  studentSj  even  at  the  Honours  stage,  are  too 
often  impressed  with  the  idea  that  the  atomic 
weight  can  be  directly  settled  by  this  process  alone, 


A tomic   Weights —  Classification        5  7 

and  seem  to  be  ignorant  that  the  specific  heat  can 
only  be  used  by  way  of  control. 

III.  Atomic  weights  can  be  deduced  from 
equivalents  by  appeal  to  the  Periodic  Law. 

The  statement  of  the  general  principle  may  run 
thus  :  when  the  elements  are  ranged  in  a  series  in 
the  order  of  the  numerical  value  of  their  atomic 
weights,  there  is  observed  a  revival  of  the  same  or 
closely  similar  characters  periodically,  and  usually 
at  every  eighth  term.  This  principle  is  usually 
displayed  in  the  following  or  some  similar  table. 

The  utility  of  this  table  in  the  settlement  of 
atomic  weights  depends  upon  the  credence  which 
is  given  to  it.  So  many  cases  of  doubtful  atomic 
weights  have,  however,  been  submitted  to  this 
criterion,  with  results  always  tending  to  confirm 
the  law,  that  it  is  now  generally  accepted.  An 
example  or  two  of  its  application  will  suffice  to 
make  it  clear. 

The  element  tellurium  has  an  atomic  weight 
which,  deduced  from  different  experimental  esti- 
mations of  its  equivalent,  probably  lies  somewhere 
between  127  and  128. 

Tellurium  is  undoubtedly  related  to  selenion 
in  the  same  way  that  selenion  is  related  to  sulphur. 
Hence  tellurium  ought  to  stand  in  the  table  vertically 
under  selenion  ;  it  cannot  do  so  unless  a  number 
is  adopted  less  than  127,  and  therefore  differing  by 
several  units  from  the  experimental  result.  In  this 
case  the  experimental  value  has  been  set  aside  by  the 


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58     Teaching  of  Elementary  Chemistry 


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Atomic   Weights — Classification        59 

majority  of  chemists  in  favour  of  the  theoretical, 
because  it  is  thought  to  be  more  likely  that  an 
undetected  source  of  error  has  attended  the  expe- 
riments than  that  the  statement  of  the  law  should 
be  at  fault. 

The  element  beryllium  is  a  metal  which  was 
formerly  supposed,  chiefly  on  the  evidence  of  the 
specific  heat  ("445  at  10°  to  100°),  to  have  the 
atomic  weight  13-5,  but  it  was  observed  that  there 
is  no  place  in  the  scheme  for  an  element  having 
the  combination  of  properties  exhibited  by  beryl- 
lium associated  with  such  a  value  for  the  atomic 
weight.  Then  it  was  discovered  that  the  specific 
heat  of  beryllium  is  anomalous  in  the  same  sense 
as  the  specific  heats  of  boron,  carbon,  and  silicon 
especially,  and,  in  a  minor  degree,  of  several  other 
elements  of  comparatively  low  atomic  weight. 
Redeterminations  of  the  specific  heat  of  beryllium 
at  higher  temperatures  ("62  at  400°  to  500°),  and 
applications  of  these  values  in  the  formula  express- 
ing the  law  of  Dulong  and  Petit,  led  to  the  value 
9*  i  for  the  atomic  weight,  and  this  is  now  uni- 
versally adopted.  This  value  is  confirmed  by  the 
vapour  density  of  the  chloride.  Hence  beryllium 
is  now  recognised  as  the  first  term  of  the  series  to 
which  magnesium  belongs. 

When,  therefore,  the  equivalent  of  an  element 
is  known,  and  a  question  is  proposed  as  to  its  atomic 
weight,  the  answer  may  be  obtained  not  only  by 
referring  to  the  specific  heat,  but  by  recalling  the 


60     Teaching  of  Elementary  Chemistry 

chief  properties  of  the  element,  and  then  considering 
whether,  having  such  properties,  it  can  possibly 
occupy  the  position  which  would  be  assigned  to  it 
if  the  equivalent  is  accepted  as  equal  to  the  atomic 
weight.  Take  the  case  of  magnesium,  the  equivalent 
of  which  is  I2'i.  Magnesium  is  a  light  metal, 
forming  one  salifiable  oxide  which  is  insoluble  in 
water ;  it  forms  a  sulphate  which  crystallises  in 
prisms  containing  water  of  crystallisation,  and 
having  the  same  form  as  sulphate  of  zinc.  On 
referring  to  the  table  we  see  that  there  is  no  place 
between  carbon  and  nitrogen  available  for  any 
element,  and  that  there  is  no  element  in  any  of  the 
columns  headed  by  boron,  carbon,  or  nitrogen  which 
exhibits  properties  similar  to  those  of  magnesium. 
But  the  isomorphism  of  the  sulphate  with  sulphate 
of  zinc  at  once  gives  the  clue,  and  we  see  that  the 
equivalent  must  be  doubled  in  order  to  supply  the 
value  of  the  atomic  weight.  Magnesium  with  the 
value  24*2  or  thereabouts  then  naturally  falls  into 
place  as  the  first  term  of  the  series  of  which  zinc 
and  cadmium  are  the  succeeding  members. 

The  confidence  placed  in  this  table  of  the 
elements  is  based  upon  the  belief  that  the  properties 
of  the  elements  are  intimately  dependent  upon  their 
atomic  weights,  that  the  number  of  elements  is 
limited,  and  that  their  atomic  weights  can  have 
only  certain  values.  All  experience  in  the  past 
certainly  tends  to  support  this  view.  Thus  in  1871 
the  places  in  the  table  now  occupied  by  gallium, 


Atomic   Weights — Classification        61 

germanium,  and  scandium  were  vacant.  These 
three  elements  have  Since  been  recognised  with  the 
properties  attributed  to  them  from  a  consideration 
of  their  position  in  the  table.1 

There  is  a  strong  analogy  between  this  manner 
of  displaying  the  connection  between  the  elements 
and  their  atomic  weights  and  the  process  of  group- 
ing the  compounds  of  carbon  into  homologous 
series.  Fifty  years  ago  a  considerable  number  of 
hydrocarbons,  alcohols,  aldehyds,  bases  &c.  were 
known,  but  for  the  most  part  they  were  known  only 
as  individual  substances  without  recognisable  rela- 
tions to  one  another.  Then  it  was  remarked,  first 
by  Schiel,  and  afterwards  by  Dumas,  that  the 
radicles  of  the  alcohol  and  of  the  fatty  acids 
exhibited  a  regularity  of  composition,  and  that  the 
properties  of  the  substances  themselves  which 
formed  the  series  were  only  gradually  modified  in 
passing  from  term  to  term.  Hence  wood  spirit, 
common  alcohol,  and  fusel  oil  were  found  to  be 
related  to  another,  and  even  such  apparently  dis- 
similar substances  as  formic  acid  and  stearic  acid 
were  recognised  as  terms  of  the  same  '  homo- 
logous '  series. 

The  arrangement  of  the  elements  themselves 
into  groups  of  closely  related  members  of  the  same 
type,  with  properties  gradually  modified  through 
successive  terms,  was  a  discovery  of  the  same  order, 

1  For  a  fuller  exposition,  see  MendeleefFs  *  Principles  of 
Chemistry,'  vol.  ii. 


62     Teaching  of  Elementary  Chemistry 

and  since,  as  pointed  out  by  Dumas,  the  values  of 
the  atomic  weights  exhibit  the  same  kind  of  rela- 
tions to  one  another  as  the  atomic  weights  of  the 
radicles  in  successive  terms  of  a  homologous  series, 
the  analogy  is  very  remarkable.  A  single  example 
will  suffice : 


(a  =  7    d=i6) 

Atomic  weight. 

Lithium     ....     a 
Sodium      .    .     .     .     a  +  d 


(a  =15     d=i4) 

Atomic  weight. 

Methyl a 

Ethyl a  +  d 


Potassium      .    .    .    a  +  2d    |    Propyl  .    .    .    .    .    a  +  2d 

Now  the  several  short  series  of  elements  when 
placed  in  parallel  columns,  as  in  the  table  given 
above,  stand  towards  another  in  much  the  same 
position  as  heterologous  series  of  carbon  compounds ; 
except,  of  course,  that  while  the  latter  can  be  trans- 
formed into  one  another,  the  former  cannot. 

The  periodic  law,  then,  is  based  upon  and 
includes  the  results  of  the  earlier  attempts  at 
classification  of  the  elements.  All  classification  is 
founded  upon  the  recognition  of  resemblances  and 
differences,  upon  finding  similarity  in  the  midst  of 
diversity  ;  but  to  be  useful  a  system  must  be  based 
upon  a  record  of  as  many  points  of  resemblance  as 
possible.  Classification,  therefore,  implies,  first,  the 
practical  process  of  observation,  and,  secondly, 
the  survey  of  many  observations,  with  a  view  to 
finding  resemblances,  so  constituting  the  logical 
process  of  induction.  In  looking  for  indications 
of  relationships,  some  considerable  experience  is 


Atomic   Weights — Classification        63 

necessary  in  many  cases  in  order  to  select  rightly 
among  the  phenomena  observed  and  to  assign  to 
each  its  share  of  importance,  so  as  to  escape  from 
the  delusions  to  which  the  observer  is  exposed  who 
gives  too  much  attention  to  differences  of  colour, 
of  density,  or  of  mechanical  condition.  It  is  pro- 
bably difficult  for  a  young  student  to  recognise 
at  first  the  close  relation  subsisting  between  such 
substances  as  chlorine,  bromine,  and  iodine.  That 
a  green  gas  should  have  much  connection  with  a 
black  shining  solid,  or  even  with  a  red  liquid, 
doubtless  appears  at  first  a  difficult  proposition  ; 
and  the  conception  that  these  three  substances 
form  a  family  having  common  features  with  minor 
differences  comes  only  after  the  characters  of  a 
homologous  series  have  been  realised.  It  is  on 
this  account  unfortunate  that  so-called  Organic 
Chemistry  should  be  separated  from  Inorganic 
Chemistry  so  rigidly  as  it  commonly  is  by  teachers, 
text-books,  and  boards  of  examiners.  The  idea 
may,  however,  be  gained  by  the  study  of  a  single 
series  of  hydrocarbons — namely,  the  paraffins — in 
which  the  relation  of  physical  properties  such  as 
volatility,  density,  melting  point,  solubility,  to  mole- 
cular weight  can  be  readily  illustrated.  As  the  busi- 
ness of  scientific  chemistry  is  so  largely  made  up  of 
the  art  of  classification,  one  or  two  further  exam- 
ples may  be  given. 

The  word '  metal '  has  received  many  applications, 
and  even  lexicographers  seem  to  be  in  doubt  as  to 


64     Teaching  of  Elementary  Chemistry 

its  origin,  but  in  chemistry  it  possesses  a  technical 
signification  which  is  generally  recognised.  Never- 
theless it  is  remarkable  how  few  chemical  teachers 
seem  to  have  a  clear  idea  of  assigning  to  it  a 
definite  connotation,  to  judge  at  least  by  the 
answers  given  by  candidates  at  examinations. 
Few,  perhaps,  are  to  be  found  in  the  confusion  of 
mind  exhibited  by  a  student  who,  at  a  recent 
examination,  stated  that '  metals  differ  from  non- 
metals,  both  by  ending  in  um  and  having  a 
metallic  lustre/  but  the '  answers  of  the  best  show 
that  they  have  not  learnt  the  art  of  observing 
correctly  and  selecting  judiciously. 

Dr.  Percy,  in  the  Introduction  to  his  great 
work  on  Metallurgy,  says  :  '  The  term  metal,  like 
the  term  acid,  is  rather  conventional  than  strictly 
scientific/  On  the  other  hand,  Professor  Roberts- 
Austen,  in  his  '  Introduction  to  the  Study  of  Metal- 
lurgy/ remarks  that  '  the  physical  aspects  of  metals 
are  so  pronounced  as  to  render  it  difficult  to 
abandon  the  old  view  that  metals  are  sharply 
defined  from  other  elements,  and  form  a  class  by 
themselves/  The  difficulty  is  to  select  characters 
which  may  be  regarded  as  diagnostic,  marking  off 
the  members  of  the  class  from  other  bodies  which 
do  not  belong  to  it. 

The  properties  of  weight  and  lustre  seem 
formerly  to  have  made  up  the  whole  idea  of  a 
metal,  and  the  difficulty  of  getting  rid  of  established 
prejudice,  and  of  seeing  things  as  they  are,  is  illus- 


Atomic   Weights — Classification        65 

trated  in  an  amusing  way  by  the  well-known  story 
of  Dr.  Pearson,  a  friend  of  Sir  Humphry  Davy's, 
who,  on  being  shown  a  specimen  of  the  newly  dis- 
covered potassium,  and  noticing  its  lustre,  ex- 
claimed, *  Why,  of  course  it  is  a  metal — how  heavy 
it  is!' 

Obviously,  then,  high  density  is  not  a  property 
exhibited  by  all  metals,  nor  even  by  all  the  common 
metals  now  that  magnesium  and  aluminium  are 
sold  in  the  shops.  Metallic  lustre  again  is  a  quality 
exhibited  by  many  substances,  such  as  graphite, 
galena,  pyrites,  iodine,  which  are  evidently  not 
metals. 

The  following  may  be  regarded  as  the  characters 
of  the  metals  as  a  class  when  in  a  pure  state. 
All  are  more  or  less  malleable  and  ductile,  they 
are  relatively  good  conductors  of  heat  and  electricity, 
and  they  form  oxides  which,  when  not  too  rich  in 
oxygen,  are  basylous  and  interact  with  acids.  The 
metals  which  present  this  assemblage  of  characters 
also  rarely  form  compounds  with  hydrogen,  and 
such  of  these  compounds  as  are  known  are  non- 
volatile solids. 

The  elements  known,  for  want  of  a  better  name, 
as  non-metals,  though  very  diverse  in  physical 
characters,  agree  in  forming  volatile  compounds 
with  hydrogen  and  oxides  which  are,  for  the  most 
part,  capable  of  giving  rise  to  acids  by  uniting  with 
the  elements  of  water.  Natural  objects,  however, 
do  not  admit  of  classification  by  the  application  of 

F 


66     Teaching  of  Elementary  Chemistry 

any  rigid  system,  and  no  definition  can  be  accepted 
absolutely  and  without  reserve.  The  teacher  will, 
therefore,  at  the  proper  stage,  point  out  there  are 
many  elements  which  stand  in  an  intermediate 
position  between  metal  and  non-metal,  exhibiting, 
like  tellurium  and  antimony,  some  of  the  properties 
of  both  classes  of  elements. 

The  difficulty  of  arriving  at  an  agreement  con- 
cerning the  application  of  terms  is  still  more 
forcibly  displayed  in  the  case  of  the  words  acid, 
base,  salt.  Even  at  the  present  day  each  of  these 
words  is  encumbered  with  a  residue  of  ancient 
usage  from  which  it  is  almost  impossible  to  set  it 
free.  The  word  '  salt '  is  perhaps  less  difficult  now 
than  it  was  a  few  years  ago  ;  but  what  is  a  base  is 
still  a  subject  concerning  which  no  two  chemists 
seem  to  be  agreed. 

Common  salt  is  a  food  stuff  known  to  man- 
kind from  very  early  times.  The  characters  origin- 
ally recognised  were  probably  first  its  taste,  then 
perhaps  its  solubility  in  water.  But  sodium  chloride 
is  not  the  only  saline  substance  obtainable  from  the 
earth  ;  there  is  nitre  found  commonly  in  tropical 
countries  and  the  soda,  borax,  magnesium  sulphate, 
sodium  sulphate,  and  other  crystalline  deposits  on 
the  shores  of  many  lakes.  These  were  doubtless 
regarded  in  early  times  as  closely  akin  to  common 
salt  from  their  saline  taste,  solubility,  and  possibly 
also  from  their  crystalline  appearance.  Such  was 
probably  the  vague  kind  of  notion  prevailing  almost 


OFtHE 

MDTNIVERSITT 


Atomic  Weights  —  Classification        67 

down  to  the  time  of  Lavoisier.  Then  came  the 
dualistic  theory  of  salts.  Having  found  that  metals 
combine  with  oxygen,  and  that  the  products  are 
usually  capable  of  dissolving  in  acids,  with  produc- 
tion of  salts,  Lavoisier  saw  in  these  facts  the  basis 
of  a  series  of  definitions.  A  salt  is  composed  of  an 
acid  united  to  a  base  :  an  acid  is  an  oxide,  usually 
of  a  non-metallic  element  ;  a  base  is  the  oxide  of 
a  metal.  If  these  views  had  stood  the  test  of 
experience,  we  should  now  be  in  possession  of  a 
system  consistent  with  itself.  As  it  is,  this  view 
of  the  constitution  of  salts  has  been  overthrown, 
while  its  nomenclature  has  been  retained.  The 
difficulty  about  the  use  of  the  term  base  arises  from 
the  fact,  that  though  we  may  still  apply  it  to  cer- 
tain of  the  oxides  of  metals,  these  compounds  do 
not  unite  as  a  whole  with  acids,  for  water  is  now 
known  to  be  formed  in  every  case  and  eliminated 
as  a  bye  product  The  essential  components  of 
the  idea  of  a  base  were  in  Lavoisier's  time  (i) 
that  it  was  an  oxide,  and  (2)  that  it  entered  into 
combination  with  an  acid,  tending  to  neutralise  it 
The  only  substances  which  enter  wholly  into  union 
with  acids  are  ammonia  and  its  derivatives  :  these 
are  the  only  true  basesy  but  they  do  not  contain 
oxygen.  It  is  not  very  creditable  to  the  leaders 
among  chemists  that  this  state  of  confusion  in  a 
comparatively  important  part  of  chemical  nomen- 
clature, otherwise  reasonable  and  consistent,  should 
be  allowed  to  continue. 


68     Teaching  of  Elementary  Chemistry 

As  to  '  acid/  everyone  now  admits  that  this 
term  is  included  under  '  salt ; '  and  to  the  question 
*  what  is  an  acid  ? '  a  complete  and  legitimate 
answer  would  be  'a  salt  of  hydrogen/  For- 
tunately we  now  possess  a  criterion  by  which  a 
salt  can  be  defined,  no  matter  whether  it  be  repre- 
sented by  the  now  obsolete  dualistic  symbol,  or 
by  the  unitary  or  by  the  more  modern  structural 
formula. 

Sodium  sulphate,  for  example,  is  Na2O.SO3  or 
Na2SO4  or  (NaO)2SO2. 

The  question  whether  it  is  a  salt  is  now  re- 
solved by  another — Does  it  readily  enter  into  double 
decomposition,  and  is  it  an  electrolyte  ?  By  this 
test  we  can  at  once  distinguish  salts  from  other 
compounds  which  in  formula  resemble  them  ; 
thus  sodium  chloride,  NaCl,  is  a  salt;  carbon 
chloride,  CC14,  is  not  a  salt. 

On  the  other  hand,  if  this  criterion  is  accepted, 
metallic  oxides  and  hydroxides,  the  compounds  to 
which  commonly  the  term  base  is  applied,  come 
under  the  same  category,  caustic  potash  being 
nearly  as  good  an  electrolyte  as  hydrochloric 
acid. 

These  subjects  are  still  undergoing  investiga- 
tion, and  chemists  are  far  from  being  united  in  the 
interpretation  of  experimental  results.  The  teacher 
will  do  well  to  study  current  literature,  and  con- 
sider carefully  the  facts  for  himself. 

While,   according   to   the    experience   of    the 


Atomic  Weights — Classification       69 

author,  it  is  unwise  to  communicate  unsettled  ques- 
tions to  mere  beginners,  as  tending  only  to  con- 
fusion and  adding  to  their  difficulties,  it  is  impera- 
tive that  all  the  facts  leading  up  to  any  generalisa- 
tion should  be  laid  without  reserve  before  advanced 
students.  They  should  be  encouraged  to  judge 
of  evidence  and  draw  conclusions  for  themselves, 
being  instructed,  however,  that,  no  matter  how 
firmly  established  or  complete  a  theory  (  =  a  view) 
or  hypothesis  (  =  supposition)  may  seem  to  be,  it 
is  never  final,  and  is  certain  to  be  sooner  or  later 
absorbed  into  a  more  comprehensive  system.  One 
of  the  greatest  evils  of  working  wholly  by  text- 
books without  personal  contact  with  a  teacher  who 
is  master  of  his  subject  is  that  the  student  thus 
taught  invariably  imbibes  the  idea  that  the  subject 
is  complete,  rounded  off,  and  finished,  and  he  sees 
no  room  for  further  inquiry.  This  is  not  only 
disastious  from  the  educational  point  of  view,  but 
is  a  serious  disadvantage  to  the  student  who  learns 
chemistry  for  the  sake  of  its  practical  techn:^al 
applications. 

One  word  in  conclusion.  Chemistry  cannot  be 
learnt  by  reading  alone.  There  comes  a  stage  in 
every  student's  career  when  much  reading  is  very 
necessary,  but  this  is  only  reached  after  long 
training  of  the  eye  and  the  hand.  First  of  all 
learn  to  see  things  clearly,  and  from  first  to  last  let 
fact  stand  before  all  hypothesis. 


APPENDIX 


EXTRACTS  FROM  THE  SYLLABUS  ISSUED  BY  THE 
DEPARTMENT  OF  SCIENCE  AND  ART,    1895. 

SUBJECT  X.— INORGANIC   CHEMISTRY, 
THEORETICAL. 

FIRST  STAGE  OR  ELEMENTARY  COURSE. 

Chemical  distinguished  from  physical  changes.  In- 
destructibility of  matter.  Decomposible  and  undecom- 
posible  substances.  Action  of  heated  copper  and 
mercury  on  air.  Action  of  heated  iron  on  steam.  Gas 
formed  by  action  of  iron  on  steam  passed  over  product 
of  heating  copper  in  air  gives  water.  Action  of  metals  on 
hydrochloric  acid  gas  and  upon  solutions  of  hydrochloric 
acid  and  sulphuric  acid.  Production  of  hydrogen.  Pro- 
duction of  oxygen  from  red  mercuric  oxide.  Formation 
of  water  by  combustion  of  hydrogen  in  air  or  by  explo- 
sion with  oxygen  in  eudiometer.  Identification  of  water 
by  its  physical  and  chemical  characters.  Mixtures  dis- 
tinguished from  compounds.  Laws  of  definite  and 
multiple  combination.  Equivalents.  Estimation  of 
equivalents  illustrated  experimentally  by  deposition  of 
such  metals  as  silver  or  copper  by  zinc  or  magnesium  and 
weighing.  Physical  properties  of  gases  as  distinguished 
from  liquids  and  solids.  Boyle's  law.  Law  of  expansion 


Appendix  7 1 

of  gases  by  heat  (without  problems).  Phenomena  of 
gaseous  diffusion.  Molecules  and  atoms.  Formation 
and  properties  of  products  of  burning  carbon  in  excess  of 
air  or  oxygen.  Comparison  of  gas  so  formed  with  gas 
obtained  by  treating  chalk  &c.  with  acid.  Composition 
of  the  atmosphere  and  action  of  animal  and  vegetable  life. 
Systematic  study  of  following  elements  and  compounds, 
their  condition  in  nature,  usual  methods  of  isolation  and 
chief  properties  :  hydrogen,  oxygen,  nitrogen,  chlorine, 
hydrogen  chloride  (bromine  and  iodine  to  be  exhibited 
and  compared  with  chlorine),  sulphur,  sulphur  dioxide, 
sulphur  trioxide,  and  sulphurous  and  sulphuric  acids,  and 
a  few  of  their  most  familiar  salts,  hydrogen  sulphide, 
nitric  acid  and  chief  nitrates,  nitrous  oxide  (from  ammo- 
nium nitrate),  nitric  oxide  (from  nitric  acid  by  copper), 
ammonia,  carbon  and  its  two  oxides,  properties  common 
to  acids  in  general. 

Symbolic  notation.  Nomenclature.  Formulae  and 
equations.  Calculation  of  quantities  by  weight  from 
chemical  equations  (French  system  of  weights).  Division 
of  elements  broadly  into  metals  and  non-metals.  General 
characters  of  metals.  Basylous  oxides  and  hydroxides, 
such  as  lime,  caustic  soda,  zinc  oxide,  black  oxide  of 
copper,  and  litharge,  and  the  interaction  of  these  with 
acids  to  form  salts  and  water. 

ALTERNATIVE  FIRST  STAGE  OR  ELEMENTARY  COURSE. 
No  substantial  alteration  has  been  made  in  this  part 
of  the  Syllabus,  but  a  few  corrections  have  been  intro- 
duced into  the  phraseology. 

SECOND  STAGE  OR  ADVANCED  COURSE. 

In  addition  to  the  subjects  of  the  first  syllabus  of 
the  elementary  course,  students  presenting  themselves 


72       Teaching  of  Elementary  Chemistry 

for  the  advanced  examination  will  be  assumed  to  have 
received  instruction  in  the  following  : 

The  experimental  methods  by  which  the  composition 
of  the  following  bodies  has  been  accurately  determined  : 
water,  atmospheric  air,  hydrochloric  acid,  ammonia,  the 
gaseous  oxides  of  nitrogen,  the  oxides  of  carbon,  sul- 
phuretted hydrogen. 

Laws  of  gaseous  combination  of  elements  and  com- 
pounds. Reduction  of  gaseous  volumes  to  standard 
pressure  and  temperature.  Calculation  of  quantities  by 
volume  and  by  weight. 

Atoms  and  molecules,  atomic  and  molecular  weights. 
Law  of  Avogadro.  Atomic  and  molecular  formulae  and 
equations.  Specific  heat  and  atomic  heat  of  the  elements. 
Graphic  or  constitutional  formulae.  Atomic  value  or 
valency  of  the  elements.  Phenomena  of  dissociation. 
Classification  of  the  elements. 

WATER. — Causes  of  permanent  and  temporary  hard- 
ness in.  Modes  of  softening.  Suitability  for  domestic 
purposes.  Determination  of  composition  of  water  by 
weight  and  by  volume. 

HYDROGEN  DIOXIDE. — Its  preparation  and  pro- 
perties. 

OZONE.— Production,  properties  and  constitution. 
Occurrence  in  nature. 

ATMOSPHERIC  AIR.— Mode  of  ascertaining  exact  com- 
position of.  Carbon  dioxide,  amount  contained  in,  and 
determination  of.  Aqueous  vapour,  determination  of. 
..,  CHLORINE.— Theory  of  bleaching.  Composition  and 
preparation  of  bleaching  powder.  Oxides  and  the  follow- 
ing oxy-acids  of  chlorine,  viz.  :  Hypochlorous,  chloric 
and  perchloric  acids,  preparation,  properties,  and  com- 
position of. 

BROMINE,  and  hydrobromic  and  bromic  acids. 


Appendix  73 

IODINE,  and  hydriodic,  iodic,  and  periodic  acids. 

FLUORINE. — Hydrofluoric  acid. 

PHOSPHORUS,  its  sources  and  its  allotropic  mo.difica- 
tions  ;  its  hydrides,  chlorides,  and  oxides.  Phosphoric 
acids  and  the  phosphates.  Hypophosphorous  and  phos- 
phorous acids. 

ARSENIC  and  its  hydrides,  chlorides,  and  oxides. 
Arsenious  and  arsenic  acids.  Arsenites  and  arsenates. 
Detection  of  arsenic. 

ANTIMONY  and  BISMUTH.— Hydride,  chloride  and 
oxides  of  antimony,  chloride,  oxides  and  salts  of  bismuth 
to  be  studied  chiefly  with  the  object  of  showing  the  rela- 
tions of  these  two  elements  to  the  members  of  the  phos- 
phorus group. 

BORON,  its  occurrence  and  allotropic  modifications. 
Boron  trioxide.  Boric  acid. 

SILICON  and  silica.  Silicic  acid.  Silicon  hydride, 
silicon  fluoride.  Names  and  formulae  of  some  of  the 
more  important  silicates  (mineral). 

The  chief  properties  of  the  following  metals,  and  the 
composition  and  properties  of  their  more  important  com- 
pounds :  potassium,  sodium,  ammonium,  silver,  mercury, 
copper,  zinc,  cadmium,  magnesium,  barium,  strontium, 
calcium,  tin,  gold,  aluminium,  platinum,  lead,  chromium, 
manganese,  iron,  cobalt,  and  nickel. 

The  processes  of  formation  and  crystallisation  of  the 
chief  salts  of  these  metals  should  be  practically  de- 
monstrated, and  specimens  should  be  prepared  by  the 
students. 

Manufacturing  processes  for  the  production  of — 

Oxygen.  i     Hydrochloric  acid. 

Chlorine,  bromine,  iodine.        Nitric  acid. 

Sodium     carbonate    and 


Bleaching  powder. 
Sulphuric  acid. 


caustic  soda. 


G 


74       Teaching  of  Elementary  Chemistry 


Lime. 

Iron  and  steel. 

Copper. 

Lead. 

Mercury. 


Silver  and  gold. 
Zinc. 

Aluminium. 
Sodium. 


SUBJECT  X. /.-INORGANIC  CHEMISTRY,  PRACTICAL. 
FIRST  STAGE  OR  ELEMENTARY  COURSE. 

The  practical  knowledge  of  the  candidate  will  in  this 
stage  be  tested  both  by  a  written  and  a  practical  exa- 
mination. 

I.  The  subjects  of  the  written  examination  will 
include — 

(a)  The  preparation  of  the  elements  and  compounds 

enumerated  in  the  elementary  course  of  Sub- 
ject X.  (Theoretical),  and  the  methods  of  ex- 
perimentally demonstrating  their  properties. 

(b)  The  principal  reactions,  both  wet  and  dry,  of  the 

following :  lead,  copper,  iron,  zinc,  calcium, 
potassium,  ammonium,  carbonates,  nitrates, 
sulphates,  chlorides. 

These  questions  will,  as  much  as  possible,  be  so 
framed  as  to  prevent  answers  being  given  by  students  who 
have  obtained  their  information  merely  from  books  and 
oral  instruction.  Any  student  on  whom  it  is  intended  to 
claim  payments  in  this  stage  may  be  called  on  by  the 
inspector  of  the  Department,  when  visiting  the  Laboratory, 
to  repeat  some  of  the  experiments  which  he  has  had  the, 
opportunity  of  witnessing. 

The  value  of  the  answers  will  be  greatly  enhanced  by 
the  neatness  and  clearness  of  the .  sketches  ;  provided, 
always,  that  an  accurate  knowledge  of  the  construction 
of  the  apparatus  is  exhibited. 


Appendix  75 

*II.  The  practical  examination  may  consist  of  exercises 
selected  from  any  of  the  following  divisions  of  experi- 
mental work  : 

A. — Testing  of  two  powders  neither  of  which  will  con- 
tain more  than  two  metallic  and  one  acid  radicle  from 
the  above  list.  The  powders  will  be  soluble  in  water  or 
in  dilute  acid. 

The  experiments  made  must  be  carefully  described, 
and  the  analytical  results  clearly  stated  and  confirmed  by 
more  than  one  reaction. 

No  notes,  books,  or  analytical  tables  may  be  consulted 
during  the  examination. 

B. — Carrying  out  experiments  for  which  printed 
instructions  will  be  given  in  the  paper,  e.g.  the  observa- 
tion of  the  effects  of  heat  or  of  water,  or  acids  £c.  upon 
the  materials  supplied.  If  a  gas  is  evolved,  the  candidate 
may  be  required  to  determine  what  it  is.  [Such  a  gas 
will  always  be  one  of  those  referred  to  under  Subject  X., 
First  Stage,  and  of  which  the  properties  have  been  demon- 
strated in  the  lectures.] 

C. — Recognition  of  materials  which  have  been 
exhibited  upon  the  lecture  table,  and  the  properties  of 
which  have  been  demonstrated,  e.g.  sulphur,  iodine, 
charcoal,  manganese  dioxide,  potassium  chlorate,  nitre, 
sal-ammoniac,  &c. 

D. — Quantitative  experiments  of  a  simple  kind,  e.g.  a 
metal  or  a  salt  may  be  supplied  to  be  weighed,  dissolved 
in  acid,  and  the  amount  of  evolved  gas  measured  at  the 
temperature  of  the  Laboratory.  Or  the  carbon  dioxide  in 
a  carbonate  may  be  estimated  by  solution  in  an  acid,  and 
observation  of  the  loss  of  weight.  Or  determination  of 
the  weight  of  one  metal,  such  as  silver,  which  can  be  dis- 
placed by  another,  such  as  magnesium.  Or  experiments 
on  the  neutralisation  of  acids  or  alkalies. 


76       Teaching  of  Elementary  Chemistry 

SECOND  STAGE  OR  ADVANCED  COURSE. 

The  examination  will  consist  of  two  parts  : 

I.  A  short  written  examination  of  about  four  questions, 
with  the  object  of  testing  the  candidate's  knowledge  of 
the  theory  of  ordinary  methods  of  qualitative  analysis  and 
the  preparation  of  such  bodies   as   are  enumerated   in 
Second  Stage,  Subject  X. 

II.  A  practical  examination,  in  qualitative  and  very 
simple  quantitative  analysis.     One  or  two  substances  for 
qualitative  analysis,  each  containing  not  more  than  four 
salt  radicles,  positive  or  negative,  selected  from  the  follow- 
ing list :  silver,  lead,  mercury,  copper,  bismuth,  cadmium, 
tin,    arsenic,   antimony,    iron,    manganese,   aluminium, 
chromium,    zinc,    cobalt,    nickel,    calcium,    strontium, 
barium,    magnesium,    potassium,    sodium,    ammonium, 
oxides,  hydroxides,  chlorides,  bromides,  iodides,  fluorides, 
sulphides,  sulphites,    sulphates,    chromates,  carbonates, 
phosphates,  arsenates,  borates,  nitrates,  nitrites,  chlorates, 
permanganates. 

There  might,  therefore,  be  four  metals  in  the  form  of 
oxide,  or  three  metals  in  the  form  of  the  same  salt,  or  two 
simple  salts  or  one  metal  in  the  form  of  three  salts. 

One  substance  may  be  given  to  be  tested  quantita- 
tively by  means  of  a  previously  prepared  volumetric  solution. 

The  remarks  with  respect  to  inspection  made  in  the 
Elementary  Stage  apply  also  to  this  grade. 

Three  and  a  quarter  hours  will  be  allowed  for  the 
examination  in  practical  analysis,  and  one  hour  for  the 
written  examination. 

NOTE.— Candidates  will  not  be  allowed  to  communi- 
cate with  one  another  during  the  examination,  but  the 
use  of  notes  or  text-books  of  analysis  will  be  permitted. 


Spottiswoode  &*  Co.  Printers,  Neia -street  Square^  London. 


OF  THE 

UNIVERSITY 


CLASSIFIED  CATALOGUE 


SCIENTIFIC    WORKS 


PUBLISHED    BY 


MESSRS,  LONGMANS,  GREEN,  &  CO, 

LONDON:  39  PATERNOSTER  ROW,  B.C. 

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CONTENTS. 


PAGE 

-  30 

-  26 

-  14 
24 
25 

-  10 


ADVANCED  SCIENCE  MANUALS 
AGRICULTURE  AND  GARDENING 
ASTRONOMY    -        -        -        - 
BIOLOGY 
BOTANY 

BUILDING  CONSTRUCTION       - 
CHEMISTRY     -  ^H 

DYNAMICS  ....  :-:-*<.& 
ELECTRICITY  .....  n 
ELEMENTARY  SCIENCE  MANUALS  -  30 
ENGINEERING-  -  -  -  -  12 
EVOLUTION  .....  18 
GEOLOGY  .....  17 
HEALTH  AND  HYGIENE  -  -  17 
HEAT  -  /  -  -  -  -  '>•  » 
HYDROSTATICS  -•'.."'-  -  -  6 
LIGHT  .....  -  8 
LONDON  SCIENCE  CLASS-BOOKS  -  32 
LONGMANS'  CIVIL  ENGINEERING 

SERIES  -  -  .  -  -  -  13 
MACHINE  DRAWING  AND  DESIGN  -  13 
MAGNETISM  .....  n 
MANUFACTURES  -  -  -  -  17 


PAGE 

MECHANICS  -  -  -  -  -  6 
MEDICINE  AND  SURGERY  -  -  19 
METALLURGY  —  -  -  -  14 

MINERALOGY 14 

NATURAL  HISTORY        -        -        -  18 

NAVIGATION 14 

OPTICS 8 

PHOTOGRAPHY         ....     8 

PHYSICS 5 

PHYSIOGRAPHY        -        -        -        -  17 

PHYSIOLOGY 24 

PROCTOR'S  (R.  A.)   WORKS    -        -  15 

SOUND 8 

STATICS 6 

STEAM,  OIL,  AND  GAS  ENGINES  -  9 
STRENGTH  OF  MATERIALS  -  -  12 

TECHNOLOGY 17 

TELEGRAPHY 12 

TELEPHONE    -        -  -         -  12 

TEXT-BOOKS  OF  SCIENCE  -  -  28 
THERMODYNAMICS  -  8 

TYNDALL'S  (JOHN)  WORKS  -  -  27 
WORKSHOP  APPLIANCES  -  -  14 


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CROSS    AND    BE  VAN.— CELLULOSE:    an    Outline    of    the 

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